Packaging a substrate with an LED into an interconnect structure only through top side landing pads on the substrate

ABSTRACT

Standardized photon building blocks are packaged in molded interconnect structures to form a variety of LED array products. No electrical conductors pass between the top and bottom surfaces of the substrate upon which LED dies are mounted. Microdots of highly reflective material are jetted onto the top surface. Landing pads on the top surface of the substrate are attached to contact pads disposed on the underside of a lip of the interconnect structure. In a solder reflow process, the photon building blocks self-align within the interconnect structure. Conductors in the interconnect structure are electrically coupled to the LED dies in the photon building blocks through the contact pads and landing pads. Compression molding is used to form lenses over the LED dies and leaves a flash layer of silicone covering the landing pads. The flash layer laterally above the landing pads is removed by blasting particles at the flash layer.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of, and claims priority under 35U.S.C. § 120 from, nonprovisional U.S. patent application Ser. No.15/067,145 entitled “Packaging a Substrate with an LED into anInterconnect Structure Only Through Top Side Landing Pads on theSubstrate,” filed on Mar. 10, 2016, now U.S. Pat. No. 9,653,437.Application Ser. No. 15/067,145, in turn, is a continuation of, andclaims priority under 35 U.S.C. § 120 from, nonprovisional U.S. patentapplication Ser. No. 14/813,277 entitled “Packaging Photon BuildingBlocks Having Only Top Side Connections In A Molded InterconnectStructure,” filed on Jul. 30, 2015, now U.S. Pat. No. 9,312,465.Application Ser. No. 14/813,277, in turn, is a continuation of, andclaims priority under 35 U.S.C. § 120 from, nonprovisional U.S. patentapplication Ser. No. 14/156,617 entitled “Packaging Photon BuildingBlocks Having Only Top Side Connections In A Molded InterconnectStructure,” filed on Jan. 16, 2014, now U.S. Pat. No. 9,130,139.Application Ser. No. 14/156,617, in turn, is a continuation of, andclaims priority under 35 U.S.C. § 120 from, nonprovisional U.S. patentapplication Ser. No. 13/441,903 entitled “Packaging Photon BuildingBlocks Having Only Top Side Connections In A Molded InterconnectStructure,” filed on Apr. 8, 2012, now U.S. Pat. No. 8,652,860, which inturn is a continuation-in-part of, and claims priority under 35 U.S.C. §120 from, the following three nonprovisional U.S. patent applications:patent application Ser. No. 12/987,148 entitled “Packaging PhotonBuilding Blocks Having Only Top Side Connections in an InterconnectStructure,” filed on Jan. 9, 2011, now U.S. Pat. No. 8,354,684; patentapplication Ser. No. 13/284,835 entitled “Jetting a Highly ReflectiveLayer onto an LED Assembly,” filed on Oct. 28, 2011, now U.S. Pat. No.9,461,023; and patent application Ser. No. 13/304,769 entitled“Micro-Bead Blasting Process for Removing a Silicone Flash Layer,” filedon Nov. 28, 2011, now U.S. Pat. No. 8,536,605. In addition, applicationSer. No. 13/441,903 claims priority under 35 U.S.C. § 119 from U.S.provisional patent application Ser. No. 61/594,371 entitled “PackagingPhoton Building Blocks Having Only Top Side Connections in a MoldedInterconnect Structure,” filed on Feb. 2, 2012. The subject matter ofeach of the aforementioned patent documents is incorporated herein byreference.

TECHNICAL FIELD

The present invention relates generally to packaging light-emittingdiodes and, more specifically, to a photon building block that can bepackaged alone as an emitter or together with other photon buildingblocks as an array of emitters.

BACKGROUND INFORMATION

A light emitting diode (LED) is a solid state device that convertselectrical energy to light. Light is emitted from active layers ofsemiconductor material sandwiched between oppositely doped layers when avoltage is applied across the doped layers. In order to use an LED chip,the chip is typically enclosed in a package that focuses the light andthat protects the chip from being damaged. The LED package typicallyincludes contact pads on the bottom for electrically connecting the LEDpackage to an external circuit. Conventionally, an LED chip is designedto be packaged either as a discrete light emitter or with a group of LEDchips in an array. The LED chip of the discrete light emitter istypically mounted on a carrier substrate, which in turn is mounted on aprinted circuit board. The LED chips of the array, however, aretypically mounted directed on the printed circuit board without usingthe carrier substrate.

Array products are not conventionally made using the discrete lightemitters as building blocks. The carrier substrate of the discrete lightemitter is typically considered needlessly to occupy space on theprinted circuit board under an array. Moreover, conducting through-holevias through the carrier substrate of the discrete light emitter wouldhave to be reconfigured in order to connect properly to contact pads onthe printed circuit board for each new array design. Thus, no carrierwith a particular set of through-holes vias could be used as a standardbuilding block. The problem of the through-hole vias in the discreteemitters can be solved by electrically connecting the LED chips totraces and contact pads on the top side of the carrier substrate. Buteliminating the through-hole vias by connecting the LED chips to pads onthe top side of the carrier substrate creates the new problem of how toconnect the pads to a power source because the carrier substrate is nolonger electrically coupled to the printed circuit board below.

FIG. 1 (prior art) shows an existing array product 10 with an array oftwenty-four LED chips electrically connected to pads 11 on the top sideof a carrier substrate 12. Array product 10 is the XLamp® MP-L EasyWhiteproduct manufactured by Cree, Inc. of Durham, N.C. In FIG. 1, carriersubstrate 12 is mounted on a metal disk 13 as opposed to on a printedcircuit board. Carrier substrate 12 is attached to metal disk 13 usingthermal glue 14. Array product 10 is inelegantly connected to power byhand soldering individual wires of the positive 15 and negative 16 powercord leads to the pads 11. Array product 10 has no features thatfacilitate connecting the pads 11 on the top side of carrier substrate12 to a power source in the board or plate below. And array product 10is not configured to be incorporated into a group of array products.

When LEDs are packaged in arrays as opposed to as discrete lightemitters, the LED chips of the arrays are mounted directly on a printedcircuit board without the carrier substrate conventionally used withdiscrete light emitters. The LED chips packaged as arrays areelectrically connected to contact pads and to traces in a top tracelayer of the printed circuit board. The LED chips are wire bonded to thetraces on the top side of the printed circuit board. The printed circuitboard is then segmented to form discrete array light sources. Largerexposed areas of the traces on the top side form contact pads to whichsupply power is connected to each discrete array light source.

The LEDs are typically covered with a layer of phosphor before the arraylight sources on the printed circuit board are segmented or singulated.The phosphor converts a portion of the blue light generated by the LEDsto light in the yellow region of the optical spectrum. The combinationof the blue and yellow light is perceived as “white” light by a humanobserver. Before the array light sources are segmented, the LEDs aretypically covered by a layer of silicone that is formed into a lensabove each light source. The layer of silicone also protects the LEDchips and top-side wire bonds.

A slurry containing the phosphor has been conventionally dispensedmanually into a ring or dam around the LED chips of each array lightsource. Then injection molding or casting molding has been used to forma lens above each array light source. The manufacturing process for LEDlight sources has been improved by combining the steps of dispensing thephosphor and forming the lens. By adding the phosphor to the silicone,the separate step of dispensing phosphor can be eliminated, and lensesare formed with phosphor dispersed throughout each lens. The lenses areformed using injection molding in which lens cavities that contain theLED dies are filled with the lens material, and the excess lens materialis squeezed out of a leakage path.

When casting molding is used, a phosphor silicone slurry is firstdispensed into the bottom half of each cavity, and then the top half ofthe cavity closes to define the lens structure and squeezes out theexcessive lens material. The injection molding and casting moldingprocesses have multiple disadvantages. First, the phosphor and thesilicone are expensive, and the lens material that is squeezed out ofthe cavities is wasted. Second, the quality of the lenses formed withinjection molding and casting molding is low because bubbles andnonuniformities remain in the finished product.

Fabricating an LED lens using these techniques is expensive becausethere are significant material losses and because non-standardsemiconductor packaging technologies and equipment are used to packagethe lens. Therefore, systems and methods that reduce manufacturing costsby reducing waste and by making it easier to package LED dies/arraysusing standard semiconductor packaging technologies and equipment aresought. In addition, systems and methods that enable LED package sizesto be shrunk to smaller sizes and to be handled using semiconductorpackaging technologies and equipment are also sought.

SUMMARY

Systems and methods for manufacturing and processing LED devices usingstandard semiconductor packaging technologies and equipment aredisclosed. The systems and methods enable LED package sizes to be shrunkto sizes that are smaller than can be made using conventional LEDpackaging technologies. In addition, a more efficient and less costlyinterface interconnect between an LED die/array and the packaging isdisclosed.

A method of fabricating an LED system involves forming a lens over LEDdies on a substrate with top-side contacts and then exposing thetop-side contacts. The top-side contacts are disposed only on the topsurface of the substrate. The substrate is provided with an array of LEDdies disposed on the top surface of the substrate such that electricalconnections to the array of LED dies are made only through the top-sidecontacts. The lens is formed over at least one of the LED dies usingcompression molding to shape a material that is disposed oversubstantially all of the top surface of the substrate. The top-sidecontacts that are covered by the material are then exposed byselectively removing the material from areas above the top-sidecontacts.

Another method of fabricating an LED system involves forming a lens overLED dies on a substrate, removing material from top-side contacts, andthen cutting the substrate from a closed board. Electrical connectionsto the LED dies are made only through the top-side contacts. A moldedlens is formed over LED dies that are disposed on the top surface of thesubstrate. The molded lens is formed using molding to shape a materialthat is disposed over substantially all of the top surface of thesubstrate. The material is then removed from areas above the top-sidecontacts, which are disposed only on the top surface of the substrate.The substrate is then cut from the closed board. The cutting leaves apattern around all four sides of the singulated substrate. Thus, theentire perimeter of the substrate has a cut pattern, such as a v-cutpattern, a saw-blade cut pattern, a laser cut pattern, a punch-cutpattern, or a water-jet-cut pattern.

In embodiments where compression molding is used to form lenses ofsilicone over LED arrays on a metal core printed circuit board (MCPCB),a flash layer of silicone is left behind covering the contact pads thatare later required to connect the arrays to power. A method for removingthe silicone flash layer involves blasting abrasive particles in astream of air at the silicone flash layer. The particles can be made ofsodium bicarbonate, sodium sulfate, ammonium bicarbonate, silicondioxide, aluminum oxide, or plastic or glass beads. The abrasiveparticles have a median diameter that is between forty and sixtymicrons. A nozzle is positioned within thirty millimeters of the topsurface of the flash layer. The flow of air is generated by compressingthe air to a pressure of more than one hundred pounds per square inchand allowing the compressed air to escape from a nozzle that has adiameter of less than two millimeters. The stream of air that exits fromthe nozzle is directed towards the top surface at an angle between fiveand thirty degrees away from normal to the top surface. The abrasiveparticles are added to the stream of air such that the particles arecarried by the stream of air. The particles then collide into the topsurface of the flash layer of silicone until the flash layer laterallyabove the contact pads is removed.

In some embodiments, an LED array light source includes LED dies mountedon a MCPCB and a lens above the LED dies formed from a layer ofsilicone. The MCPCB has a trace layer and a solder mask layer. The LEDdies are electrically coupled to the trace layer. The solder mask layeris disposed over the trace layer. A contact pad is formed on the tracelayer by an opening in the solder mask. The layer of silicone that isdisposed over the LED dies forms an edge around the contact pad. Thelayer of silicone is not present laterally above the contact pad. Thelayer of silicone contains a trace amount of a blasting medium at theedge of the layer of silicone. The blasting medium is sodiumbicarbonate, sodium sulfate, or ammonium bicarbonate. The layer ofsilicone can also contain phosphor. The trace amount of the blastingmedium is embedded into the edge of the silicone around the contact padwhen a flash layer of silicone is removed from above the contact pad byblasting abrasive particles of the blasting medium in a stream of air atthe silicone flash layer.

In another embodiment, an LED array light source includes a printedcircuit board (PCB), an LED die, a contact pad, and a layer of silicone.The PCB has a top side, a bottom side, and four top edges. The LED dieand the contact pad are disposed on the top side of the PCB. The layerof silicone is disposed over the LED die and extends to each top edge ofthe PCB. However, the layer of silicone is not disposed laterally abovea portion of the contact pad because the silicone has been removed byblasting abrasive particles in a stream of air at the layer of silicone.

In yet another embodiment, a high-pressure stream of water is used toremove the flash layer of silicone over the contact pads. The water ispressurized to a pressure of over fifty pounds per square inch and thenforced through a nozzle with a diameter of less than one millimeter. Thepressurized stream of water is aimed directly at the silicone flashlayer over the contact pads until the flash layer is removed.Alternatively to using pure water, abrasive particles made of silica,aluminum oxide, or garnet can be added to the stream of water to allowthe deflashing process to be performed at a lower water pressurecompared to using pure water.

In some embodiments, standardized photon building blocks are used tomake both discrete light emitters with one building block as well asarray products with multiple building blocks. Each photon building blockhas one or more LED chips mounted on a carrier substrate. No electricalconductors pass between the top and bottom surfaces of the substrate.The photon building blocks are held in place by an interconnectstructure that is attached to a heat sink. Examples of the interconnectstructure include a molded interconnect device (MID), a lead framedevice or a printed circuit board.

Landing pads on the top surface of the substrate of each photon buildingblock are attached to contact pads disposed on the underside of a lip ofthe interconnect structure using solder or an adhesive. The lip extendsover the substrate within the lateral boundary of the substrate. In asolder or SAC reflow process, the photon building blocks self-alignwithin the interconnect structure. Molten SAC or solder alloy of thelanding pads wets the metal plated contact pads, and the surface tensionof the molten alloy pulls the landing pads under the contact pads.Conductors on the interconnect structure are electrically coupled to theLED dice in the photon building blocks through the contact pads andlanding pads. The bottom surface of the interconnect structure iscoplanar with the bottom surfaces of the substrates of the photonbuilding blocks.

In some embodiments for array products, the substrates of multiplephoton building blocks are supported by the interconnect structure. Thesubstrates of all of the photon building blocks have substantiallyidentical dimensions. A thermal interface material is placed on theupper surface of a heat sink, and the bottom surface of the interconnectstructure contacts the thermal interface material. The interconnectstructure is fastened to the heat sink by bolts that pass through holesin the interconnect structure.

A method of making both a discrete light emitter and an array product,which uses the same standardized photon building blocks supported by aninterconnect structure, includes the step of mounting an LED die on acarrier substrate that has no electrical conductors passing from its topsurface to its bottom surface. A landing pad on the top surface of thesubstrate is placed under and adjacent to a contact pad disposed on theunderside of a lip of the interconnect structure. In order to place thelanding pad under the contact pad, the lip of the interconnect structureis placed over the top surface of the substrate and within the lateralboundary of the substrate.

A conductor disposed on or in an interconnect structure is electricallyconnecting to an LED die on a photon building block by bonding a landingpad to a contact pad. A landing pad can be bonded to a contact pad byheating the metal alloy of the landing pad such that the landing padaligns with the metal contact pad. Alternatively, the landing pad can bebonded to the contact pad using anisotropic conductive adhesive film(ACF) technology. After the landing pad is aligned with and bonded tothe contact pad, the bottom surface of the substrate is substantiallycoplanar with the bottom surface of the interconnect structure.

When this method is used to make an array product with multiple photonbuilding blocks, a second lip of the interconnect structure is placedover the top surface of the substrate of a second photon building block,and a second landing pad on the second substrate is placed under andadjacent to a second contact pad under a lip of the interconnectstructure. The second substrate of the second photon building block hasdimensions that are substantially identical to those of the substrate ofthe first photon building block. A second conductor of the interconnectstructure is electrically connected to a second LED die on the secondphoton building block by bonding the second landing pad to the secondcontact pad. After the second landing pad is bonded to the secondcontact pad, the bottom surface of the substrate of the second photonbuilding block is substantially coplanar to the bottom surface of theinterconnect structure.

A thermal interface material is then placed over the upper surface of aheat sink. The bottom surfaces of the interconnect structure and of thesubstrates of the photon building blocks are placed over the thermalinterface material.

In some embodiments, a novel light emitting device includes an LED diedisposed above a substrate that includes no electrical conductorsbetween the top and bottom surfaces of the substrate. The device alsoincludes a means for electrically coupling the LED die to a conductorlocated outside the lateral boundary of the substrate. The meanscontacts a landing pad disposed on the top surface of the substrate. Thelanding pad aligns the substrate to a contact pad on the means when thelanding pad is heated. The means has a bottom surface that is coplanarwith the bottom surface of the substrate.

After any die attach and wire bonding steps in the manufacturing of anarray-based LED assembly, a layer of Highly Reflective (HR) material isdeposited around the LED dice to coat the upper surface of thesubstrate. In one example, the HR material is deposited with precisionby jetting microdots of the HR material in liquid form onto selectedportions of the upper surface of the substrate, thereby forming a layerof HR material that is thick enough (at least 10 microns thick) to havea reflectivity of at least 85 percent.

Limits on mechanical tolerances can lead to physical differences betweenthe LED assemblies being manufactured. LED dice may differ slightly insize, and LED dice may be placed in slightly different locations fromone LED assembly to the next. In accordance with some embodiments,machine imaging is usable to detect such physical differences from LEDassembly to LED assembly and to control the jetting process to adjustfor such physical differences so that in each LED assembly beingmanufactured substantially all of the upper substrate surface that isnot covered with an LED die is coated with HR material.

In one example, each microdot of HR material has a diameter of less than100 microns and is typically 50-80 microns in diameter. The HR materialhas an adequately low viscosity (less than 1100 cP) such that it flowslaterally to some degree once it reaches the substrate surface. Due tothe lateral flow of the HR material, the HR material can be made (1) toflow under bridging wire bonds and to coat the substrate underneath thewire bonds, (2) to reach and to wet side edges of the LED dice, or (3)to reach and to wet the inside side edge of a phosphor retaining ring.In one example, the area of substrate between LED dice is not coatedwith HR material in order to reduce manufacturing time. Because the HRmaterial is only deposited after die attach and after wire bonding,fiducial markers on the upper surface of the substrate (that wouldotherwise be covered and obscured by HR material were conventionalscreen printing used to deposit the HR material) are observable andusable during die attach and wire bonding. The depositing of the HRlayer by jetting microdots of HR material results in a reduction in theamount of exposed substrate area that is not covered with HR material.Reducing the amount of exposed substrate area that is not covered withHR material serves to improve the light efficiency of the resulting LEDassembly.

Further details and embodiments and techniques are described in thedetailed description below. This summary does not purport to define theinvention. The invention is defined by the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, where like numerals indicate like components,illustrate embodiments of the invention.

FIG. 1 (prior art) is a perspective view of an existing array productwith multiple LED chips electrically connected to pads on the top sideof a carrier substrate.

FIG. 2 is a cross sectional view of an LED system with an array of LEDdies and top-side contacts disposed on the top surface of a substrateaccording to one embodiment of the invention.

FIG. 3 is a flowchart illustrating a method of fabricating an LED systemwith a compression-molded lens and exposed top-side contacts.

FIG. 4 is a cross sectional view of an LED system with a molded lens andtop side contacts exposed using deflashing.

FIG. 5 is a flowchart illustrating a method of fabricating an LED systemwith a molded lens and top side contacts exposed using deflashing.

FIG. 6A is a perspective view of an LED system with a molded lens, anarray of LED dies and exposed top-side contacts that has been separatedfrom a closed board and has a v-cut pattern around its entire perimeter.

FIG. 6B is a cross sectional bubble view of a portion of the v-cutperimeter of the LED system of FIG. 6A.

FIGS. 7A-B shows laser-cut patterns on sides of substrates formed when alaser is used to separate an LED system from a closed board.

FIG. 8A shows a saw-blade cut pattern on the side of a substrate formedby dicing a closed board using a saw blade.

FIG. 8B is a cross-sectional perspective view of a punch-cut patternformed on a substrate by punching a closed board using a punchapparatus.

FIG. 8C shows a punch cut pattern on the side of a substrate formed bypunching a closed board using a punch apparatus.

FIG. 8D shows a substrate being cut with a water jet.

FIG. 8E shows a water jetting cut pattern on the side of a substrateformed by cutting the substrate using a water jet apparatus.

FIG. 9 is a flowchart illustrating a method of fabricating an LED systemwith a molded lens and exposed top-side contacts by separating the LEDsystem from a closed board.

FIG. 10 is a top view of a metal core printed circuit board (MCPCB) onwhich multiple arrays of LED dies are mounted.

FIG. 11 is a top view of the MCPCB of FIG. 10 on which areas have beenmarked to show where a flash layer should be removed to expose contactpads.

FIG. 12 is a cross sectional view of the MCPCB of FIG. 10 showing theflash layer that is to be removed using the novel blasting process.

FIG. 13 is a more detailed view of the flash layer of FIG. 12.

FIG. 14 is a flowchart of steps of a method for removing a flash layerof silicone that covers contact pads without damaging the contact pads.

FIG. 15 is a cross sectional view illustrating blasting particlescolliding with a flash layer at a blasting site enclosed by a blastingmask.

FIG. 16 is a cross sectional view of the blasting sites of FIG. 12 afterthe flash layer has been removed using the method of FIG. 14.

FIG. 17 is a top view of another MCPCB from which a flash layer ofsilicone is to be removed using the method of FIG. 14.

FIG. 18 is a top-down perspective view of a blasting site between fourlenses on the MCPCB of FIG. 17.

FIG. 19 is a perspective view of a discrete light source with top-sideelectrical contacts from which a flash silicone layer has been removed.

FIG. 20 is a cross-sectional view of a novel photon building blocksupported by an interconnect structure.

FIG. 21 is a more detailed view of a contact pad connected to a landingpad as shown in FIG. 20.

FIG. 22A is a cross-sectional view of a conductor on an interconnectstructure coupled through a contact pad to a landing pad on a substrate.

FIG. 22B is a perspective view of the path of the conductor of FIG. 22Apassing through a hollow via to the contact pad.

FIG. 22C is a perspective view of the conductor of FIG. 22A passingthrough and entirely covering the inside surface of a hollow via.

FIG. 23 is a cross-sectional view of the conductor of FIG. 22A passingaround the rounded edge of a lip of the interconnect structure.

FIG. 24 shows a landing pad on the substrate bonded to a contact pad onthe underside of a lip of the interconnect structure by an anisotropicconductive adhesive (ACF).

FIG. 25 shows a lead frame interconnect structure with a metal foillayer that functions both as a conductor of the interconnect structureand as a contact pad that bonds to a landing pad on the substrate.

FIG. 26 shows an interconnect structure made from a printed circuitboard with a metal layer that functions both as a conductor of theinterconnect structure and as a contact pad that bonds to a landing padon the substrate.

FIG. 27 is a top view of a photon building block that includes four LEDdice surrounded by four landing pads.

FIG. 28 is a top view of another implementation of a photon buildingblock that includes four LED dice surrounded by two landing pads.

FIG. 29A is a top view of two photon building blocks in an interconnectstructure built into an array product.

FIG. 29B is a cross-sectional view through line B-B of the array productshown in FIG. 29A.

FIG. 29C is a cross-sectional view through line C-C of the array productshown in FIG. 29A.

FIG. 30A is a more detailed view of the connection between the landingpad of the substrate and the contact pad of the interconnect structureshown in FIG. 29A.

FIG. 30B shows the contact pad FIG. 30A without the landing pad below.

FIG. 31 is a perspective view of four photon building blocks in aninterconnect structure built into an array product.

FIG. 32 is a flowchart of steps for making both a discrete light emitterand an array product using the same standardized photon building blocks.

FIG. 33A is a perspective view of another embodiment of a photonbuilding block containing a plurality of LED dies.

FIG. 33B shows another embodiment of photon building block of FIG. 33Ain which the LED dies are not connected by wire bonds all the way to thelanding pads.

FIG. 33C is a perspective view of the photon building block of FIG. 33Bthat includes a micro-lens centered over each LED die.

FIG. 34A is a cross-sectional view of the photon building block of FIG.33B being supported by an interconnect structure solely through landingpads on the upper surface of the substrate.

FIG. 34B is a cross-sectional view of the photon building block of FIG.33A being supported solely through landing pads on the upper surface ofthe substrate.

FIG. 35A is perspective view of the bottom surface of an hexagonalstar-shaped molded interconnect structure.

FIG. 35B is a top perspective view of the molded interconnect structureof FIG. 35A supporting the photon building block of FIG. 33C.

FIG. 36A is a top perspective view of a packaged LED array in which aphoton building block is supported by a hexagonal molded leadframestructure.

FIG. 36B is a bottom perspective view of the indentation on the bottomside of the molded leadframe structure of FIG. 36A into which a photonbuilding block fits.

FIG. 37A is a perspective view of a hexagonal molded interconnectstructure with surface conductive paths supporting the photon buildingblock of FIG. 33C.

FIG. 37B is a perspective view of an hexagonal molded interconnectstructure with inner lead frame conductors.

FIG. 37C is a perspective view of the bottom side of the moldedinterconnect structure of FIG. 37B showing contact pads formed from theleadframe conductors.

FIG. 38 is a perspective view of a lead frame reel with templates ofconductors such as those in the molded interconnect structure of FIG.37C.

FIG. 39 (prior art) is top-down diagram of one type of conventional LEDassembly.

FIG. 40 (prior art) is a simplified cross-sectional side view of the LEDassembly of FIG. 39.

FIG. 41 (prior art) is a top-down diagram of a panel of metal coreprinted circuit boards (MCPCBs).

FIG. 42 (prior art) is a top-down diagram of the die placement area ofan MCPCB of FIG. 42 before die placement.

FIG. 43 (prior art) is a diagram of a screen printing mask used to applya highly reflective (HR) material onto the die placement area of FIG.42.

FIG. 44 (prior art) is a top-down diagram of the die placement area ofFIG. 42 after deposition of the HR material.

FIG. 45 (prior art) is a top-down diagram of the die placement area ofFIG. 44 after die attach has been completed.

FIG. 46 (prior art) is a top-down diagram of the die placement area ofFIG. 45 after wire bonding has been completed.

FIG. 47 (prior art) is a top-down diagram of the die placement area ofFIG. 46 after formation of a phosphor retaining ring.

FIG. 48 (prior art) is a top-down diagram of the die placement area ofFIG. 47 after placement of phosphor within the retaining ring.

FIG. 49 is a top-down diagram of a white LED assembly in accordance withone novel aspect.

FIG. 50 is a simplified cross-sectional side view of the white LEDassembly of FIG. 49.

FIG. 51 is a top-down diagram of a panel of MCPCBs of which the MCPCB ofFIG. 50 is one.

FIG. 52 is a top-down diagram of the die placement area of the MCPCB ofFIG. 50.

FIG. 53 is a top-down diagram of the placement area of FIG. 52 after dieattach has been completed.

FIG. 54 is a top-down diagram of the placement area of FIG. 53 afterwire bonding has been completed.

FIG. 55 is a top-down diagram of the placement area of FIG. 54 afterformation of the phosphor retaining ring.

FIG. 56 is a simplified cross-sectional diagram that shows thedeposition of an HR layer by jetting microdots of HR material onto thesubstrate around and between the LED dice of the LED assembly.

FIG. 57 is a simplified top-down diagram of the die placement area afterthe jetting of the HR material has been completed.

FIG. 58 is a simplified top-down diagram of the die placement area afterphosphor has been placed over the LED dice within the confines of theretaining ring.

FIG. 59 is a simplified cross-sectional diagram of a white LED assemblywhere the LED dice are disposed in a well.

FIG. 60 is a simplified cross-sectional diagram of a white LED assemblyhaving a ceramic substrate.

FIG. 61 is a simplified cross-sectional diagram of a white LED assemblyhaving a ceramic substrate, where the HR material does not touch a sideedge of any of the LED dice, and is not disposed between the LED dice.

FIG. 62 is a flowchart of a method in accordance with a novel aspect. Ina first novel aspect, an HR layer is deposited onto the substrate of anLED assembly after die attach and after wire bonding. In a second novelaspect, an HR layer is deposited by jetting microdots of HR materialonto a substrate of the LED assembly.

DETAILED DESCRIPTION

Reference will now be made in detail to some embodiments of theinvention, examples of which are illustrated in the accompanyingdrawings.

Systems and methods for manufacturing and processing LED devices usingstandard semiconductor packaging technologies and equipment aredisclosed. The systems and methods enable LED package sizes to be shrunkto sizes that are smaller than can be made using conventional LEDpackaging technologies. In addition, a more efficient and less costlyinterface interconnect between an LED die/array and the packaging isdisclosed.

In one embodiment, an LED is fabricated by providing a substrate with anarray of LED dies and top-side contacts. One or more lenses are formedover the array of LED dies using compression molding such that one lensis formed over at least one of the LED dies. The top-side contacts areexposed by selectively removing material from areas covering thetop-side contacts. Fabricating LED lens in this manner enables low costmass production of LED dies and arrays that have an interfaceinterconnect that makes it easy to package the LED dies and arrays.

In another embodiment, an LED system is fabricated by providing asubstrate with an array of LED dies and top-side contacts. A lens isformed over the array of LED dies using compression molding, and thetop-side contacts are exposed by selectively de-flashing material fromareas covering the top-side contacts. Fabricating LED lenses in thismanner also enables low cost mass production of LED dies and arrays thathave an interface interconnect that makes it easy to package the LEDdies and arrays.

In another embodiment, an LED system is fabricated by cutting asubstrate that has an array of LED dies formed on it from a closedboard. A molded lens is formed over the array of LED dies usingcompression molding, and the plurality of top-side contacts are exposedby selectively removing material from areas above the top-side contacts.When the substrate is cut, a cut pattern is formed around the entireperimeter of the substrate because the substrate is cut from a closedboard. The substrate can be cut from the closed board using v-cutting,saw-blade cutting, laser cutting, punch cutting, water-jet cutting or acombination of these techniques. The cut pattern that surrounds theentire perimeter of the substrate has a v-cut pattern, a saw-blade cutpattern, a laser cut pattern, a punch cut pattern, a water-jet-cutpattern or a combination of these cut patterns. Fabricating an LEDsystem in this manner also reduces the cost of mass production of LEDdies on substrates that have an interface interconnect that makes iteasy to package the substrate and LED dies.

FIG. 2 is a cross sectional view of an LED system 20 with an array ofLED dies 21 disposed on the top surface 22 of a substrate 23. Top-sidecontacts 24 are also disposed on top surface 22 of substrate 23. Acompression molded lens 25 is disposed over the LED dies 21.

FIG. 3 is a flowchart illustrating steps 26-29 of a method offabricating LED system 20 with compression-molded lens 25 and top-sidecontacts 24. The first step 26 involves providing substrate 23 with thearray of LED dies 21 disposed on top surface 22 of substrate 23.Electrical connections to the array of LED dies 21 are made through aplurality of the top-side contacts 24, which are disposed only on topsurface 22 of substrate 23. In step 27, lens 25 is formed over at leastone of the LED dies 21 by using compression molding to shape a materialthat has been disposed over substantially all of top surface 22 ofsubstrate 23. In one example, the material is silicone. In theembodiment of FIG. 2, a single lens is formed over the array of LED dies21. In other embodiments, however, individual micro-lenses are formedover less than the entire array, such as over individual LED dies. Instep 28, the plurality of top-side contacts 24 are exposed byselectively removing the material that forms the lens from areascovering the top-side contacts 24. As shown in FIG. 2, the material neednot be removed from the entire area above the contacts 24. In step 29,substrate 23 is detached from the closed board of which it was a part.FIG. 2 shows substrate 23 after being detached from the closed board.

Further details regarding LEDs with compression molded lens and top-sidecontacts and methods of making them are provided below with reference toFIGS. 10-19. LED arrays with compression molded lens and top-sidecontacts can also be configured with an interface interconnect thatmakes it easier and more cost effective to package the LED dies as isfurther discussed with reference to FIGS. 20-38. FIG. 2 shows an exampleof the interface interconnect 30.

FIG. 4 is a cross sectional view of an LED system 32 with a molded lens33 and top side contacts 34 exposed using deflashing. A substrate 35with an array of LED dies 36 is disposed on a top surface 37 of thesubstrate. Electrical connections to the array of LED dies 36 are madethrough the top-side contacts 34, which are disposed only on top surface37 of substrate 35. Molded lens 33 is formed over at least one of theLED dies 36. The material used to make lens 33 is disposed oversubstantially all of top surface 37 of substrate 35 except for over thetop-side contacts 34. The material is selectively removed from the areasabove the top-side contacts 34. A plurality of solder connections 38 areformed on the plurality of top-side contacts 34. A plurality of leads 39are coupled to the plurality of solder connections 38. In FIG. 4, one ofthe leads 39 is depicted as a wire. In FIG. 2, a lead 40 that is coupledto a solder connection 38 is depicted as a contact pad that is attachedto a top-side contact 24 by the solder connection 38.

FIG. 5 is a flowchart illustrating steps 41-46 of a method offabricating LED system 32 with molded lens 33 and top side contacts 34exposed using deflashing. In a step 41, substrate 35 is provided with anarray of LED dies 36 disposed on top surface 37 of the substrate.Substrate 35 is part of a closed board. Electrical connections to theLED dies 36 are made through the top-side contacts 34 that are disposedonly on top surface 37. In step 42, molded lens 33 is formed over atleast one of the LED dies 36 using a type of molding to shape a materialthat is disposed over substantially all of top surface 37. In step 43,the top-side contacts 34 are exposed by selectively de-flashing thematerial from areas covering the top-side contacts 34. In step 44,substrate 35 is detached form the closed board. In step 45, the solderconnections 38 are formed on the top-side contacts 34. In step 46, theleads 39 are connected to the solder connections 38 such that the LEDdies 36 are connected only through the leads 39.

LED arrays with molded lens and top side contacts exposed usingdeflashing can also be configured with an interface interconnect thatmakes it easier and more cost effective to package the LED dies andarrays as is further discussed with reference to FIGS. 20-38.

FIG. 6A is a cross sectional view of an LED system 50 that has beenseparated from a closed board. LED system 50 has a molded lens 51, anarray of LED dies 52 and exposed top-side contacts 53. The LED dies 52are electrically connected only through the top-side contacts 53, whichare disposed only on the top surface 54 of a substrate 55. LED system 50has been separated from a closed board using a v-cutting process suchthat a v-cut pattern 56 is present around the entire perimeter ofsubstrate 55. Thus, the v-cut pattern 56 is present on each of the foursides 57-60 of substrate 55. Singulation of LED system 50 from theclosed board is performed by v-scribing both the top surface 54 and thebottom surface 61 and then snapping off the remaining thin portion 62 ofthe closed board that remains between the two v-cuts. The thin portion62 through the middle each side 57-60 is rougher than the cut portionsabove and below because the thin middle portion has been snapped off.

FIG. 6B is a bubble view of a portion of side 57 of LED system 50showing the v-cut pattern 56 in more detail. The thin snapped portion 62runs through the middle of the V-cut pattern 56.

In another embodiment, a laser is used to separate substrate 55 from theclosed board. FIG. 7A is a top-down view of top surface 54 showing alaser-scribed cut pattern 63 on side 57 that remains after individuallaser holes are burned along the edge that is to be cut. The laserleaves the laser-scribed cut pattern 63 around the entire perimeter ofsubstrate 55. FIG. 7B shows a laser-machined cut pattern 64 that remainson side 57 after a laser beam is run along the edge of the closed boardthat is to be cut. Laser-machined but pattern 64 is smoother thanlaser-scribed cut pattern 63. Both laser-scribed cut pattern 63 andlaser-machined cut pattern 64 are shown at the same magnification.

In yet another embodiment, a saw blade is used to separate substrate 55from the closed board. The saw blade leaves a saw-blade cut pattern 65around the entire perimeter of substrate 55, as shown in FIG. 8A. Thecurved lines on the saw-blade cut pattern 65 are left by a rotating sawblade.

In yet another embodiment, a punch apparatus is used to separatesubstrate 55 from the closed board. Punching leaves a punch cut pattern66 around the entire perimeter of substrate 55, as shown in FIGS. 8B-C.The punch cut pattern 66 includes substantially vertical lines generatedin the direction that the punch apparatus moves to cut the substrate 55.The punch cut pattern 66 can include a secondary pattern 67 thatresembles a compression left over by the punching process. The punch cutpattern can also leave a rounded corner 68 on the side that the punchapparatus impacts substrate 55. In the orientation of FIG. 8B, the punchapparatus impacts substrate 55 first from the bottom.

In yet another embodiment, a water jetting apparatus is used to separatesubstrate 55 from the closed board. As illustrated in FIG. 8D, whenwater jetting is used to cut substrate 55, garnet particles dispersed ina fluid are ejected from a nozzle and follow a curved pattern throughsubstrate 55. The curved pattern is curved in the direction opposite tothe direction of the water jet motion. Cutting substrate 55 with a waterjet leaves a water-jet cut pattern 69 around the entire perimeter ofsubstrate 55, as shown in FIG. 8E. The water-jet cut pattern 69 iscurved from top to bottom with the top being the surface of substrate 55that the water jet particles impact first (i.e., the side of thesubstrate on which the water jet is located).

FIG. 9 is a flowchart illustrating steps 73-77 of a method offabricating LED system 50 with molded lens 51 and exposed top-sidecontacts 53 by separating LED system 50 from a closed board. In step 73,molded lens 51 is formed over LED dies 52 that are disposed on topsurface 54 of substrate 55. Molded lens 51 is formed using molding toshape a material that is disposed over substantially all of top surface54 of substrate 55. In step 74, the material is removed from areas abovetop-side contacts 53. In step 75, substrate 55 is cut from a closedboard. The cutting of substrate 55 is performed using a technique suchas v-cutting, dicing with a saw blade, laser cutting, punch cutting orwater-jet cutting. In step 76, solder connections are formed on top-sidecontacts 53. In step 77, leads are connected to the solder connections.Electrical connections to the LED dies 52 are made only through theleads and top-side contacts 53.

Further details of LED systems with molded lenses and top side contactsand methods of making them from closed boards are provided below withreference to FIGS. 10-19 and 39-62. The LED systems can also beconfigured with an interface interconnect that makes it easier and morecost effective to package the arrays of LED dies is discussed below withreference to FIGS. 20-38.

FIG. 10 is a top view of a metal-core printed circuit board (MCPCB) 110on which multiple arrays of LED dies 111 are mounted. Because MCPCB 110has a metal core, it would be difficult to supply power to the LED dies111 through through-hole vias that pass from the LEDs through theprinted circuit board to the bottom surface of the board. Consequently,the LED dies 111 are electrically connected to contact pads on the topside of MCPCB 110. The MCPCB 110 is then segmented to form discretearray light sources. The discrete light sources can be used asstandardized photon building blocks by packaging them in a multitude ofways using a molded interconnect structure that electrically contactsthe photon building blocks from the top side. How discrete light sourcesare packaged in a molded interconnect structure that electricallyconnects only from the top side to the discrete light sources isdescribed in detail below.

In the embodiment of FIG. 10, MCPCB 110 includes a 5×12 matrix of 4×4LED arrays. MCPCB 110 has a length of about 250 mm and a width of about75 mm. Each LED array is later segmented into a square of the MCPCB thatis 11.5 mm on a side. Thus, MCPCB 110 has a very high density of lightsources per area of the printed circuit board. There are less than threemillimeters of space on the board between the edge of the lens thatcovers the LED dies 111 and the edge of each of the segmented squarelight source. At each corner of the square is a contact pad 112 that isused to supply power to the array light source. The contact pads 112 areformed by exposing large triangular areas of a trace layer. The tracelayer is covered by a solder mask layer 113 of hardened epoxy. Holes insolder mask layer 113 form the contact pads 112 and the locations on thetrace layer below to which the LED dies 111 are wire bonded.

A lens is formed over each LED array using compression molding.Compression molding can be used because there are no holes or openingfrom the top side to the bottom side of MCPCB 110 through which highpressure molding material could escape. Thus, MCPCB 110 is a closedboard. Conventional printed circuit boards used to mount LED arrays havepunch-outs or etchings cuts to isolate the electrical leads of each LEDarray. MCPCB 110, on the other hand, is a closed board with no punchouts, holes or etching cuts through the board. The very high density ofcomponents and the closed board of MCPCB 110 are conducive tocompression molding. A single molding chamber is formed over the top ofMCPCB 110 by sealing the chamber around the border 114 of MCPCB 110. Asmall space is maintained between solder mask layer 113 and the moldcover to allow the molding material to flow freely between theindividual cavities above the LED arrays. In the actual molding process,MCPCB 110 is inverted and lowered into the mold cover, which containsthe lens cavities. The molding material is pumped into the singlemolding chamber under pressure and fills all of the crevices of thecavities without leaving bubbles or nonuniformities in the hardenedmolding material. The molding material that fills the small spacebetween the mold cover and solder mask layer 113 forms a thin flashlayer that covers the contact pads 112 that must later be electricallycoupled to the interconnect packaging structure.

In one embodiment, the molding material is a slurry of phosphorparticles in silicone. The phosphor is evenly dispersed throughout thesilicone and converts a portion of the blue light generated by the LEDsinto light in the yellow and red regions of the optical spectrum. Theblue light from the LEDs and the yellow and red light from the phosphorcombine to yield white light, which is optically spread out by thesurface of the lens. After the lenses are formed using compressionmolding, the individual LED array light sources are segmented by cuttingMCPCB 110 into squares. It is more efficient, however, first to removethe flash layer that covers the contact pads 112 before segmenting MCPCB110 into individual LED array light sources.

FIG. 11 is a top view of MCPCB 110 of FIG. 2 on which areas have beenmarked to show where the flash layer should be removed to expose thecontact pads 112. For a unit size of 11.5 mm by 11.5 mm for the LEDarray light sources of FIG. 2, the contact pads 112 can be cleaned ofthe silicone flash layer by removing silicone from 5 mm by 5 mm squares.A novel micro-bead blasting process is used to remove the silicone flashlayer from the square blasting sites 115.

FIG. 12 is a cross sectional view of MCPCB 110 of FIG. 2 showing theflash layer 116 that is to be removed using the novel blasting process.MCPCB 110 has a thick solid aluminum base 117. For example, aluminumbase 117 is 1.6 mm thick. A dielectric layer 118 separates aluminum base117 from the trace layer 119 that forms the contact pads 112. Dielectriclayer 118 has a thickness of about twenty microns (micrometers or μm).Trace layer 119 does not entirely cover dielectric layer 118, but ratheris formed by patterned traces separated by dielectric material. Soldermask layer 113 covers trace layer 119 and has openings only over thecontact pads 112 and the locations at which the LED dies 111 are wirebonded to traces.

The molded silicone forms lenses 120 over the arrays of LED dies 111. Inthe embodiment of FIG. 12, the diameter of lens 120 is about twice aslong as each side of the 4×4 array of LED dies so as to allow most ofthe emitted light to reach the surface of lens 120 within the criticalangle required for the light to escape from the lens. The height of thelens 120 is about 1.5 mm from solder mask layer 113. Other embodimentshave lenses of different sizes and shapes over the LED dies 111. Forexample, the silicone above each LED array can have a small overallcurvature that is covered by many smaller micro-structures, such ashemispheres or pyramids. Alternatively, the lens shape can have a dimpleabove the middle of each LED array.

FIG. 13 is a more detailed view of flash layer 116 of FIG. 12. FIG. 13shows that flash layer 116 is relatively thick compared to trace layer119. Whereas in some compression molding processes flash layer 116 has athickness between fifty to one hundred microns, trace layer 119 can havea thickness of less than five microns. Trace layer 119 typically hasthree sublayers: a thicker lower layer of copper, a thinner middle layerof nickel, and a thinner upper layer of either gold or silver. Copper isless expensive than nickel, gold or silver, so the traces are comprisedmostly of copper. The upper layer of gold or silver is required becauseit is difficult to solder the wire bonds directly to copper. The middlelayer of nickel is used to attach the gold or silver to the thickercopper layer because gold and silver do not readily adhere directly tocopper. The copper is typically 2-80 microns thick, the nickel istypically 1-3 microns thick, and the gold or silver is typically 1-5microns thick. Thus, the contact pads 112 will be damaged if the gold orsilver that is no thicker than five microns is removed from the uppersurface of the trace layer 119. The novel micro-bead blasting processprovides a way of removing silicone flash layer that is about fiftymicrons thick without removing the upper layer of trace layer 119, whichis only about one tenth as thick.

FIG. 14 is a flowchart illustrating steps 121-125 of a micro-beadblasting process that removes a flash layer of silicone that coverscontact pads without damaging the contact pads. The steps of the methodof FIG. 14 are described in relation to FIG. 13.

In a first step 121, the flash layer 116 is formed over the printedcircuit board 110 using compression molding. Although the flash layer116 of FIG. 13 results from compression molding silicone, othertransparent molding materials may also be used, such as epoxy. The flashlayer of silicone 116 in FIG. 13 is disposed above two contact pads 112.

In step 122, a nozzle 127 is positioned within thirty millimeters of atop surface 128 of flash layer 116. In order to clean a blasting site115 that is 5 mm by 5 mm square, the method of FIG. 14 uses a nozzle 127that has a diameter of about two millimeters and that is placed abouttwenty-two millimeters above top surface 128. A smaller nozzle diameterwould be used to remove a flash layer from a smaller blasting site, inwhich case the nozzle would be positioned closer to the top surface ofthe flash layer. For example, in order to clean the flash layer from ablasting site 115 having a diameter of two millimeters located betweenLED arrays having unit sizes of five millimeters on a side, nozzle 127would have a diameter of about 0.5 millimeters and would be positionedabout two millimeters above the top surface 128 of flash layer 116. Theblasting site is located over the contact pads 112 that are to becleaned of flash layer 116. Positioning nozzle 127 farther away from topsurface 128 allows the stream of air exiting the nozzle to spread outinto a wider plume 129 before contacting top surface 128. Thus, nozzle127 must be positioned closer to top surface 128 in order to maintainthe stream of air within a smaller blasting site 115.

In step 123, the flow of air that exits nozzle 127 is directed at topsurface 128 of flash layer 116 within blasting site 115. The stream ofair that exits from nozzle 127 is directed towards top surface 128 at anangle that is between five and thirty degrees away from a normal angleto the top surface. The stream of air is generated by compressing theair to a pressure of more than one hundred pounds per square inch (psi)and then allowing the compressed air to escape from nozzle 127. In orderto clean a blasting site 115 that is 5 mm by 5 mm square, the flow ofair is generated by compressing the air to a pressure between onehundred and one hundred forty pounds per square inch and then allowingthe compressed air to escape from a nozzle that has a diameter of lessthan two millimeters.

In step 124, blasting particles 130 of a blasting medium are added tothe stream of air such that the particles are carried by the stream ofair and collide into top surface 128 of flash layer 116 above contactpad 112. The blasting particles 130 are also called micro beads,although they need not be spherically shaped. The blasting medium shouldhave a Mohs hardness of less than three; sodium bicarbonate (NaHCO₃),sodium sulfate and ammonium bicarbonate (ammonium hydrogen carbonate,(NH₄HCO₃)) can be used. In one embodiment, the blasting particles 130are monoclinic prisms of sodium bicarbonate that have been purified andsorted through a sieve to have a uniform particle size of about fiftymicrons in the longest dimension. The blasting particles 130 are storedas a powder and are added into the flow of air by a mixer 131 shortlybefore exiting nozzle 127.

When cleaning a blasting site 115 that is 5 mm by 5 mm square, thenozzle can be placed about twenty-two millimeters above top surface 128,which allows the blasting particles 130 to achieve their highestvelocity. When the particles 130 are first added to the flow of air bymixer 131, the inertia of the particles prevents them from immediatelyaccelerating to the speed of the air flow. However, within abouttwenty-two millimeters, the particles 130 have accelerated to the speedof the stream of air and have achieved their highest velocity. Atdistances greater than about thirty millimeters from nozzle 127,resistance from ambient air overcomes the thrust from the stream of airand slows down the particles 130. At distances less than about twentymillimeters from nozzle 127, the particles 130 have not yet acceleratedto the speed of the flow of air. Thus, where particles of about fiftymicrons in length are used, flash layer 116 can be removed in theshortest period of time by blasting the particles from a distance ofabout twenty-two millimeters because the particles possess the mostamount of kinetic energy at that distance from the nozzle.

In step 125, the particles 130 are collided into flash layer 116 untilthe flash layer laterally above contact pad 112 is removed. Theparticles 130 have facets and edges that rip the silicone of the flashlayer 116 apart. Then the air blows the ripped pieces of silicone away.Small amounts of sodium bicarbonate remain embedded in the silicone thathas not been removed. When cleaning the relatively large blasting sites115 of FIG. 11, nozzle 127 may be placed at about twenty-two millimetersfrom top surface 128 of flash layer 116, which permits the particles 130to acquire their maximum kinetic energy. Consequently, the flash layerin the blasting sites 115 that are squares 5 mm on a side can be removedin a relatively short 2-3 seconds. On the other hand, when cleaning therelatively small blasting site 115 having a diameter of two millimeterslocated between LED arrays having unit sizes of five millimeters on aside, nozzle 127 must be placed a relatively close two millimeters fromtop surface 128, which does not permit the particles 130 to achievetheir maximum speed. Consequently, the flash layer in a blasting sitewith a diameter of two millimeters can be removed only after arelatively long eight seconds of blasting.

The stream of air exiting nozzle 127 is not directed in step 123 towardsflash layer 116 at an angle normal to top surface 128, i.e., the streamof air is not directed orthogonally to top surface 128. Instead, thestream of air is directed towards flash layer 116 at an angle that isbetween five and thirty degrees away from normal to the top surface inorder to permit the particles 130 to be blown away from the blastingsite. If the nozzle were to be directed orthogonally to the top surfaceof the flash layer, the blasting particles would bounce straight back upand collide with the particles in the stream of air. This would reducethe force by which the blasting particles collide with the flash layer.In addition, the particles would not bounce sideways after striking thetop surface and therefore would not be carried out of the blasting siteand would build up. On the other hand, if the nozzle were directed at ashallow angle to the top surface of the flash layer, such as an anglegreater than thirty degrees from normal, then the vector of the particlespeed normal to the top surface would be insufficient to remove theflash layer. The particles would tend to be deflected by the top surfaceand would not break into the surface.

Even at a steeper angle of incidence, such as ten degrees, the blastingparticles 130 are more likely to bounce off of top surface 128 insteadof breaking into the surface when flash layer 116 is thicker. At thebeginning of the blasting process when flash layer 116 is still aboutfifty microns thick, the particles 130 are more likely to bounce off topsurface 128 because the thicker silicone flash layer can elasticallycompress to absorb the impact of the particles. As flash layer 116 iseaten away and becomes thinner, the rate of silicone removal becomesfaster as the kinetic energy of the particles increasingly tears thesilicone as opposed to being absorbed by the silicone.

Current compression molding techniques specify that the thickness of aflash layer of silicone can be fifty ±25% microns. It is desirable tokeep the flash layer as thin as possible to save on silicone but yetallow the silicone to flow freely between the individual lens cavitiesto achieve high quality lens structures. Where the flash layer isthinner than thirty microns, the elasticity of the silicone layer isreduced to the point that blasting particles do not readily bounce offof the silicone but rather tear the silicone. As even thinner flashlayers become possible, the flow of compressed air alone will besufficient to remove the flash layer from between the lens structures.

FIG. 15 illustrates blasting particles at a blasting site that isenclosed by a blasting mask 132. Blasting mask 132 is made of stainlesssteel and is about 200-500 microns thick. Mask 132 is used when thelenses are particularly close to the blasting sites 115 and must beprotected from the blasting particles 130. For example, blasting mask132 is used for blasting sites located between LED arrays having unitsizes of five millimeters on a side. The blasting process is sped up byusing a mask because the flow of air need not be turned off when movingfrom site to site. Each lens 120 is protected from the blastingparticles 130 by mask 132 as the stream of air moves over the lens to anew blasting site. In contrast, where no blasting mask is used withlarger unit sizes, such as an array unit size of 11.5 mm on a side, theflow of air is turned off as the position of the nozzle is moved fromone blasting site to another in order to avoid damaging the lensstructures.

Using a blasting mask, however, creates other complications that slowdown the blasting process. The thickness of the blasting mask creates awell that both (i) obstructs the corners of the blasting site from beingreached by the stream of air and (ii) hinders the blasting particlesfrom being blown away from the blasting site. First, the blasting maskobstructs the nearest corner of the blasting site from direct blastingby the angled stream of air. Thus, the far side of the blasting site 115is cleaned first, and then MCPCB 110 is rotated to permit the cleaningof the other side of the blasting site. The rotation and double pass ofthe stream of air slow the blasting process. Second, the sides 133 ofthe blasting mask 132 form a deep well that tends to trap the blastingparticles 130. If blasting particles 130 from the stream of air collidewith other particles that previously accumulated over the surface of theblasting site 115, then the silicone flash layer 116 will not be tornand ultimately removed. Thus, the angle of the stream of air isincreased towards thirty degrees from normal to top surface 128 in orderto bounce the particles 130 away from the incoming particles and out ofthe well. In addition, the pressure of the air used to generate thestream of air is increased towards one hundred forty pounds per squareinch in order to provide the particles with enough kinetic energy tobounce out of the well.

FIG. 16 is a cross sectional view of the blasting sites 115 of FIG. 12after the flash layers 116 have been removed using the method of FIG.14. FIG. 16 shows that after the blasting process, the layer of siliconeforms an edge 134 around the contact pads 112 that have been cleaned.Some of the blasting particles 130 break apart in the blasting processand form dust having particles sizes much smaller than 50 microns. Someof the dust lodges in the silicone around the blasting sites 115. Thus,the silicone at edge 134 contains a trace amount of the blasting medium,such as sodium bicarbonate, that remains from the blasting particles130. The trace amount of sodium bicarbonate can be detected in thesegmented LED array light sources using a gas spectrometer.

FIG. 17 is a top view of another MCPCB 135 from which a flash layer ofsilicone is removed using the method of FIG. 14. In FIG. 17, the lenses136 and flash layer 137 have already been formed by compression molding.Like MCPCB 110 of FIG. 2, MCPCB 135 also includes a 5×12 matrix of LEDarrays. And each LED array is later segmented into a square of the MCPCBthat is 11.5 mm on a side. Unlike MCPCB 110 of FIG. 2, however, thecontact pads 138 on MCPCB 135 are not formed by exposing areas of atrace layer that is covered by a solder mask layer. Instead, the contactpads 138 are four strips of metal that extend out from under each lens136. The flash layer 137 covers the metal strips.

FIG. 18 is a top-down perspective view of a blasting site 139 betweenfour lenses 136 on MCPCB 135. The micro-bead blasting process wasperformed using a 0.077 inch diameter nozzle positioned about 22millimeters above flash layer 137. A pressure of 120 psi was used togenerate the stream of air that contained particles of sodiumbicarbonate having a median diameter of about 50 microns. The stream ofair containing the blasting particles was blasted at blasting site 139for 1.65 seconds. The blasting removed material to various degreesprogressing outwards from the center of blasting site 139. At the centerof blasting site 139, the entire thickness of flash layer 137 has beenremoved, and the blasting has even removed some of the upper layer ofgold from the contact pads 138. Some of the dielectric layer was alsoremoved from the center of blasting site 139. Moving outwards from thecenter of blasting site 139, only the silicone was removed from a largeportion of the contacts pads 138 without damaging the upper layers ofthe contact pads 138. This region is marked with diagonal hashes in FIG.18. In the next region on each contact pad 138 outwards from the centerto the blasting site, the silicone flash layer 137 was not entirelyremoved from the contact pad. FIG. 18 shows areas 140 on the corners oflenses 136 that have been partially roughened by the blasting process.

In another embodiment, water-based jetting is used to remove a flashlayer of silicone. Purified water is pressurized to a pressure ofbetween fifty and one thousand pounds per square inch and then forcedthrough a nozzle with an opening diameter between one hundred and onethousand microns. The exiting water beam is aimed directly at the flashlayer over the electrical contact pads until the flash layer is removed.The combination of the water pressure and nozzle diameter is chosen toachieve a stream of water with enough momentum to break the siliconeflash layer but yet that leaves the metal trace layer undamaged.Alternatively to using pure water, abrasive particles such as silica,aluminum oxide, or garnet particles can be added to the stream of waterto allow a more efficient deflashing process at a lower water pressurecompared to with pure water.

FIG. 19 is a perspective view of a discrete light source 141 with onlytop-side electrical contacts from which a flash silicone layer 116 hasbeen removed. Discrete light source 141 was manufactured using themethod of FIG. 14. Discrete light source 141 results from thesegmentation of the arrays of LED dies 111 mounted on MCPCB 110 of FIG.2. The printed circuit board (PCB) segment 142 of discrete light source141 has a top side 143, a bottom side 144, and four edges 146-149. Alight emitting diode die 150 is disposed on the top side 143 of PCBsegment 142. A contact pad 112 is also disposed on the top side 143 ofPCB segment 142. A layer of silicone 116 is disposed over LED die 150and extends to each of the edges 146-149 of PCB segment 142 except wherethe silicone flash layer 116 has been removed through blasting. Thelayer of silicone 116 is not disposed laterally above a portion ofcontact pad 112 at blasting site 115. In the embodiment of FIG. 19, thesilicone flash layer 116 has not been removed from the entire surface ofcontact pad 112; a small portion of the trace layer that forms contactpad 112 remains covered by silicone.

All of the electrical contacts on discrete light source 141 are on thetop side 143. Thus, PCB segment 142 has no electrical contacts on thebottom side 144. The layer of silicone 116 forms lens 120 above LED 150.There are less than three millimeters between the edge 145 of lens 120and any of the edges 146-149 of PCB segment 142 because discrete lightsource 141 was segmented from a high density printed circuit board 110.There are also less than three millimeters between the edges 146-149 ofPCB segment 142 and any of the LED dies in the array of LED dies. Thereare no holes that pass from the top side 143 to the bottom side 144 ofPCB segment 142. Any punch-outs, through holes, or etching cuts in thetop side 143 of discrete light source 141 would have hampered theformation of lens 120 using compression molding because the pressurizedmolding material would have escaped through the holes. The silicone atthe edge of blasting site 115 contains a trace amount of the blastingmedium that remains embedded in the silicone.

FIG. 20 is a cross-sectional view of a photon building block 204supported by an interconnect structure 205. Photon building block 204includes a substrate 206 upon which an LED die 207 is mounted. Substrate206 is non-conductive ceramic. In another implementation, substrate 206is crystalline silicon. Landing pads 208 are disposed on the top surface209 of substrate 206. No electrical conductor passes from the topsurface 209 of substrate 206 to the bottom surface 210 of substrate 206.LED die 207 is electrically coupled to power solely through the landingpads 208. Thermal interface materials are disposed between LED die 207and substrate 206. A first layer 211 of thermal interface material (TIM)is made of the same material and deposited in the same process aslanding pads 208. In one implementation, pads 208 and first layer 211are traces made of a Cu—Ni—Au alloy or a Cu—Ni—Ag alloy. A second layer212 of thermal interface material is deposited on first layer 211. Inone implementation, second layer 212 is a silver-filled epoxy. LED die207 is bonded through second layer 212 and first layer 211 to topsurface 209 of substrate 206.

LED die 207 is electrically connected through wire bonds 213 to landingpads 208. A thin conformal layer of a wavelength conversion material,such as a phosphor, is formed over LED die 207. Then a clear resinencapsulant, such as silicone, is overmolded over LED die 207 and thewire bonds 213 from about the middle of a landing pad 208 on one side ofupper surface 209 of substrate 206 to about the middle of a landing pad208 on the opposite side of upper surface 209. The silicone forms theshape of a lens 214. Photon building block 204 includes substrate 206,the landing pads 208 and everything encapsulated by lens 214.

Interconnect structure 205 supports photon building block 204 throughthe landing pads 208. The landing pads 208 are both electrically andmechanically connected to contact pads 215 disposed on the underside ofa lip of the interconnect structure 205. In one implementation, landingpads 208 are attached to contact pads 215 by a solder paste. An exampleof a solder paste is a SAC alloy, such as SAC 305 (96.5% Sn, 3.0% Ag,0.5% Cu). In another implementation, landing pads 208 are attached tocontact pads 215 by an adhesive. An example of an adhesive is ananisotropic conductive adhesive associated with anisotropic conductivefilm (ACF) technology. In the embodiment of FIG. 20, landing pads areelectrically and mechanically connected to contact pads 215 by solder232.

In the embodiment of FIG. 20, contact pads 215 are electricallyconnected to conductive traces 216 on the top surface 217 ofinterconnect structure 205 by through-hole vias 218. Thus, eachconductive trace 216 is electrically coupled to LED die 207 through via218, contact pad 215, solder 232, landing pad 208 and wire bond 213.Interconnect structure 205 has a bottom surface 219 that issubstantially coplanar with bottom surface 210 of substrate 206.

Photon building block 204 and interconnect structure 205 are attachedover a third layer 220 of thermal interface material (TIM) to a heatsink 221. In one implementation, third layer 220 of thermal interfacematerial is thermal glue. In another implementation, third layer 220 ismade of thermal grease, and interconnect structure 205 is attached toheat sink 221 by bolts 222. Any small deviations of bottom surfaces 210and 219 from being exactly coplanar are compensated by the thickness ofthe thermal interface material, such as the thermal grease. Bolts 222hold interconnect structure 205 in place over heat sink 221, and photonbuilding block 204 is held in place by the connection between landingpads 208 and contact pads 215. Thus, substrate 206 is thermally coupledthrough the third layer 220 of TIM to heat sink 221. In oneimplementation, bottom surface 210 of substrate 206 is not directlyconnected to heat sink 221, but is rather “floating” in the layer 220 ofthermal grease. Photon building block 204 is mechanically connected toheat sink 221 only through the bonds between landing pads 208 andcontact pads 215. In contrast, carrier substrate 12 of the prior artarray product 10 is attached to the heat sink only by gluing orsoldering the bottom surface of substrate 12 to the heat sink.

Compared to a conventional discrete light emitter, a printed circuitboard (PCB) and one layer of TIM have been removed from beneath novelphoton building block 204. In a conventional discrete light emitter, thecarrier substrate sits on a TIM layer over a metal core PCB, which inturn sits on another TIM layer over the heat sink. Using the novelphoton building blocks to make an array product is more economical thanmaking an array product using conventional discrete light emittersbecause the cost of the metal core PCB and an additional TIM layer issaved. Moreover, heat generated by the LED die is more effectivelytransferred from the carrier substrate through one TIM layer directly tothe heat sink than through an additional MCPCB and TIM layer ofconventional discrete light emitters.

In another embodiment, photon building block 204 and interconnectstructure 205 are not attached directly to heat sink 221 over third TIMlayer 220. Instead, a thermal spreader is placed between heat sink 221and photon building block 204. Photon building block 204 andinterconnect structure 205 are then attached over third TIM layer 220 tothe thermal spreader. An example of a thermal spreader is a vaporchamber.

FIG. 21 shows one of the contact pads 215 of FIG. 20 in more detail andthe landing pad 208 to which the contact pad is connected. Contact pad215 is a metal trace on interconnect structure 205. In oneimplementation, interconnect structure 205 is a molded interconnectdevice (MID). MID 205 is a three-dimensional electronic circuit carrierproduced by injecting a metalized, high-temperature thermoplastic, suchas liquid crystal polymer (LCP), into a mold. A laser writes the path ofthe trace on the surface of MID 205. Where the laser beam oblates thethermoplastic, the metal additive in the thermoplastic forms a very thinconductor path. The metal particles on the conductor path form thenuclei for subsequent metallization. Metallization baths are used toform successive layers of copper, nickel and/or gold traces on theconductor path. For example, a layer of copper forms on the conductorpath when the oblated thermoplastic is placed in a copper bath. Whereverthe laser can oblate the surface of MID 205, three-dimensional circuittraces can quickly be formed.

Contact pad 215 is formed on the underside of a lip 223 of MID 205 afterthe laser oblates the shape of the pad. Metal trace 216 is also formedon the top surface 217 of interconnect structure 205 in the same manneras contact pad 215 is formed. Either the laser is articulated so thatthe laser beam can be directed at both top surface 217 and the undersideof a lip 223, or two lasers can be used. In the implementation of FIG.21, through-hole via 218 is filled with metal before the traces and padsare formed. The metallization baths plate the trace 216 and contact pad215 over the ends of metal via 218.

An electrical and mechanical connection is made between contact pad 215and landing pad 208 by reflowing a solder alloy between the pads. Forexample, a SAC reflow process can be performed where a Sn—Ag—Cu solderalloy is placed at the edge of landing pad 208. When the SAC solder ismelted, the solder wets the metal of contact pad 215. Then the surfacetension of the molten SAC alloy pulls landing pad 208 under contact pad215. A bond is then formed between landing pad 208 and contact pad 215when the SAC alloy cools and solidifies.

FIG. 22A shows another implementation of how a metal trace 224 on MID205 is electrically coupled to landing pad 208 on substrate 206. Insteadof via 218 filled with metal, as in FIG. 21, MID 205 of FIG. 22Aincludes a hollow tapered via 225. Hollow via 225 is formed using aconical plug in the molding process that forms the molded interconnectdevice 205. The laser oblates a conductor path across top surface 217,around the inside surface of via 225, and then on the underside of a lip223 to form the shape of contact pad 215. The conductor path and padshape are then plated in a metallization bath. FIG. 22B shows theconductor path of the laser in more detail. The conductor path can bemuch wider than the width of the laser. The laser can make many passesto create a wide conductor path, such as the one shown in FIG. 22C. InFIG. 22C, the entire partially conical-shaped inside surface of hollowvia 225 is oblated and will be plated in a metallization step.

FIG. 23 shows another implementation of how a metal trace 226 on MID 205is electrically coupled to landing pad 208 on substrate 206. Lip 223 ofMID 205 is given a rounded edge. The laser makes a continuous conductorpath across top surface 217, around the rounded edge and then on theunderside of a lip 223.

FIG. 24 shows an alternative way of electrically and mechanicallycoupling contact pad 215 to landing pad 208 that does not involvesolder. An anisotropic conductive adhesive 227 is used to connectcontact pad 215 to landing pad 208 in FIG. 24 instead of the bond formedusing solder reflow as shown in FIG. 21. Because solder is not used,photon building block 204 does not self-align within interconnectstructure 205, but must be accurately positioned before the adhesivecured. Anisotropic conductive adhesive film (ACF) technology involvesconductive balls dispersed in an adhesive. For example, Au-coatedpolymer balls or Ni-filled balls are dispersed in an epoxy adhesive. Thesurfaces being electrically coupled are then pressed together to thediameter of the balls. The adhesive is then cured, for example byheating. An electrical contact is made in those areas where the ballstouch both surfaces. The anisotropic conductive adhesive 227 is notconductive in those areas where the balls are still dispersed in thecured adhesive. In FIG. 24, the anisotropic conductive adhesive 227mechanically connects pad 215, the underside of lip 223 and the entireside of MID 205 to landing pad 208 and the side of substrate 206.However, an electrical connection is made only between those areas ofcontact pad 215 and landing pad 208 that were pressed together to withinthe diameter of the conductive balls.

FIG. 25 shows another implementation of how a conductor 228 oninterconnect structure 205 is electrically coupled to landing pad 208 onsubstrate 206 using solder. Interconnect structure 205 of FIG. 25 is alead frame instead of a molded interconnect device. A metal foil 228 isstamped in the form of the conductors, leads and “gull wings” requiredfor the package of the discrete light emitter or array product. Leadframe structure 205 is then made by injection molding a liquid crystalpolymer (LCP) 229 around a stamped metal foil 228. The metal foilfunctions both as the conductor 228 as well as the contact pad 215. Theend of the metal foil under lip 223 can be stamped in the shape of acontact pad with a shape corresponding to the shape of landing pad 208in order to facilitate self-alignment during a solder reflow process.

FIG. 26 shows another implementation of a conductor 231 in interconnectstructure 205 that is electrically coupled to landing pad 208 onsubstrate 206 using solder. Interconnect structure 205 of FIG. 24 is aprinted circuit board (PCB). For example, interconnect structure 205 isan FR-4 printed circuit board made of woven fiberglass fabric 230 withan epoxy resin binder. FR-4 PCB 205 has several metal layers. One of themetal layers 231 functions both as the conductor and as the contact pad215. The end of metal layer 231 under lip 223 can be formed in a shapecorresponding to the shape of landing pad 208 in order to facilitateself-alignment during a solder reflow process.

FIG. 27 is a top view of a photon building block 234 that includes fourLED dice 235-238. The same material is used to make the four landingpads 239-242 as well as the first TIM layer 211 beneath the four LEDs.Second layer 212 of thermal interface material is deposited on firstlayer 211 beneath each LED die and is not visible in the view of FIG.27. LED die 235 and 238 are electrically connected in series betweenlanding pads 239 and 242. Two wire bonds connect each LED die to alanding pad and to another LED die. For example, wire bonds 243-244connect LED die 235 to landing pad 239. The dashed circle indicates theextent to which silicone lens 214 encapsulates the components onsubstrate 206. Lens 214 extends to about the middle of the landing pads239-242. The diameter of lens 214 is about twice as long as each side ofthe 2×2 array of LED dice so as to allow most of the emitted light toreach the surface of lens 214 within the critical angle required for thelight to escape from the lens.

Photon building block 234 can be used to make both a discrete lightemitter with a single photon building block as well as an array productwith multiple photon building blocks. Interconnect structure 205 caneasily be molded or configured to incorporate photon building block 234into a plurality of different discrete light emitter products. The boltholes through which bolts 222 attach interconnect structure 205 to heatsink 221 can easily be repositioned without changing the design ofphoton building block 234. And the conductors that are electricallycoupled to the LED dice can easily be retraced using a laser to writethe conductive paths over the surface of the molded interconnect device.Thus, a new emitter need not be tested and qualified each time a newlight emitter product is made using photon building block 234.

FIG. 28 is a top view of a photon building block 245 with only twolanding pads 246-247 that surround the four LED dice 235-238. As withphoton building block 234 of FIG. 17, the landing pads 246-247 and thefirst TIM layer 211 beneath the four LEDs are made from the samematerial, such as a Cu—Ni—Au alloy or a Cu—Ni—Ag alloy. The landing pads246-247 have points that extend to the four corners of substrate 206. Ina SAC reflow step, the solder alloy that extends farther toward thecorners of substrate 206 than with landing pads 239-242 can moreprecisely align substrate 206 beneath the contact pads of theinterconnect structure 205. The smaller surface area of landing pads246-247 beneath the contact pads, however, results in a weakermechanical connection between the landing pads and contact pads.

FIG. 29A is a top view of photon building block 234 of FIG. 17 builtinto an array product with another photon building block 248. A moldedinterconnect device 249 holds the photon building blocks 234 and 248 inplace in a 1×2 array. The area of MID 249 is denoted by cross hatching.MID 249 has six lips that extend over the corners of photon buildingblocks 234 and 248 and hold those corners in place. For example, a lip223 of MID 249 extends over the upper right corner of substrate 206, anda contact pad on the underside of lip 223 is electrically andmechanically connected to a portion of landing pad 239 using solder oran adhesive. MID 249 also has another lip 250 that extends over both theupper left corner of photon building block 234 and the upper rightcorner of photon building block 248. Separate contacts pads under lip250 are bonded to landing pad 240 of photon building block 234 and to alanding pad 251 of photon building block 248. MID 249 has four holes 252for the bolts 222 that attach the array product to heat sink 221.

FIG. 29B is a cross-sectional view through line B-B of the 1×2 arrayproduct shown in FIG. 29A. FIG. 29B shows how contact pad 215 on theunderside of lip 223 is electrically and mechanically connected to aportion of landing pad 239. FIG. 29B also shows portions of the contactpads under lip 250 that bond to landing pads 240 and 251. FIG. 29C is across-sectional view through line C-C of the 1×2 array product shown inFIG. 29A. The contact pads of MID 249 are not visible in the crosssection of FIG. 29C.

FIGS. 30A-B illustrate the connection between landing pad 239 andcontact pad 215 of FIG. 29A in more detail. Contact pad 215 has the sameoutline shape as a corner of the landing pad 239 below. A solder reflowprocess can be performed with the contact pads on top aligning to solderon the landing pads below, or the process can be inverted. The structureof FIG. 29B can be inverted such that the landing pads are on top of thecontact pad and align to molten solder on the contact pads.

In a SAC reflow process when the SAC solder on landing pad 239 ismelted, the solder wets the metal of contact pad 215. Then the surfacetension of the molten SAC solder pulls contact pad 215 over the portionof landing pad 239 that has the same shape. The four landing pads at thecorners of substrate 206 are thereby each pulled towards the contactpads of the same shape and align photon building block 234 within theframe of MID 249. When the SAC solder cools and solidifies, bonds areformed between the landing pads and the contact pads. The solder bondsbetween the landing pads and the contact pads hold the photon buildingblocks in place such that the bottom surfaces of the substrates aresubstantially coplanar with bottom surface 219 of MID 249 even when thearray product is not attached to a heat sink. The array product can beshipped unattached to any submount, such as a heat sink. The bondsbetween the landing pads and the contact pads are sufficiently strong tomaintain the mechanical integrity of the array product despite thevibrations and bumping usually encountered in shipping.

FIG. 30A also shows a conductor 253 on the top surface of MID 249 thatis electrically coupled to first LED die 235. Conductor 253 is a metaltrace formed by plating a path oblated by a laser. Metal trace 253 iselectrically coupled to LED die 235 through a solid metal via 254,contact pad 215, solder 232 or an ACF adhesive, landing pad 239 and wirebonds 243-244. The dashed line designates the extent of silicone lens214.

FIG. 30B shows contact pad 215 of FIG. 30A without the landing pad 239of photon building block 234 below. The triangular cross-hatched areaaround contact pad 215 is lip 223 that extends over the upper rightcorner of substrate 206 of photon building block 234. FIG. 30B alsoshows a lip 255 of MID 249 that extends over the lower right corner ofsubstrate 206. The area of MID 249 shown with a latticed pattern isfilled with liquid crystal polymer from top surface 217 to bottomsurface 219 of the interconnect structure.

FIG. 31 is a perspective view of photon building block 234 of FIG. 17built into an array product with three other photon building blocks. Amolded interconnect device 256 holds the photon building blocks in placein a 2×2 array. The interconnect structure 256 includes bridges betweenthe photon building blocks that support a center island 257 beneathwhich the contact pads attach to the inner landing pads of the fourphoton building blocks. As MID 256 is formed in a molding process,non-planar surfaces are easily made. MID 256 has curved walls 258 aroundthe photon building blocks that are coated with a reflective material,such as a metal film. The curved walls can be shaped to impart aparabolic reflection to the light emitted from the photon buildingblocks. The conductors that connect to the contact pads (not shown inFIG. 31) are drawn with a laser over the curved walls and then plated ina metallization bath. The conductors are connected to the contact padswith through hole vias or hollow vias as shown in FIGS. 21-22. AlthoughFIG. 31 depicts a 2×2 array of photon building blocks supported by aninterconnect structure, arrays with other dimensions can also be made ina similar manner using bridges between the photon building blocks.

FIG. 32 is a flowchart illustrating steps 259-265 of a method of makingboth a discrete light emitter and an array product using the samestandardized photon building blocks that have one or more LED chipsmounted on a carrier substrate. The method can be used to connect photonbuilding blocks in any configuration, such as in parallel or in series,to achieve the desired light output and power consumption of theresulting array product. The method easily connects the photon buildingblocks electrically, mechanically and thermally to other structures ofthe ultimate lighting product. The electrical connections to the powersource can easily be configured. The orientation of the photon buildingblocks can easily be aligned with reflectors and lenses of the lightingproduct. The position of the bolts that mechanically connect theinterconnect structure to the lighting product can easily bereconfigured without changing the photon building blocks. And theinterconnect structure can easily be configured to thermally connectwith a multitude of heat sinks.

In a first step 259, light emitting diode die 235 is mounted on carriersubstrate 206 of first photon building block 234. Substrate 206 has noelectrical conductors passing from its top surface 209 to its bottomsurface 210. LED die 235 is attached to substrate 206 using first TIMlayer 211 and second TIM layer 212. Landing pad 239 on top surface 209of substrate 206 is made from the same material and in the same processas first TIM layer 211.

In step 260, landing pad 239 is placed under and adjacent to contact pad215, which is disposed on the underside of lip 223 of interconnectstructure 249. In so doing, lip 223 is placed over top surface 209 ofsubstrate 206 and within the lateral boundary of substrate 206. At theconclusion of step 260, the photon building blocks are placed withininterconnect structure 249.

In step 261, conductor 216 of interconnect structure 249 is electricallyconnecting to LED die 235 by bonding landing pad 239 to contact pad 215.The pads are bonded by either solder or an ACF adhesive. When usingsolder, landing pad 239 is bonded to contact pad 215 by heating a metalalloy on landing pad 239 such that the landing pad aligns with the metalcontact pad. When using anisotropic conductive adhesive film (ACF)technology to bond the pads, the photon building blocks are accuratelypositioned within interconnect structure 249, and landing pad 239 isbonded to contact pad 215 when the ACF adhesive is cured by heating.After landing pad 239 is aligned with and bonded to contact pad 215,bottom surface 210 of substrate 206 is substantially coplanar withbottom surface 219 of interconnect structure 249.

In step 262, when the method of FIG. 32 is used to make an arrayproduct, second lip 250 of interconnect structure 249 is placed over thetop surface of a second substrate, and a second landing pad 251 isplaced under and adjacent to a second contact pad attached to theunderside of lip 250. The second substrate is part of second photonbuilding block 248 and has dimensions that are substantially identicalto those of the first substrate 206. A second LED die disposed on thesecond substrate has dimensions that are substantially identical tothose of LED die 235 on first substrate 206.

In step 263, when the method of FIG. 32 is used to make an arrayproduct, a second conductor of interconnect structure 249 iselectrically connected to the second LED die that is disposed on thesecond substrate by bonding second landing pad 251 to the second contactpad attached to the underside of lip 250. For example, landing pad 251can be bonded to the second contact pad using a SAC reflow process or byusing an anisotropic conductive adhesive. After second lip 250 is placedover the top surface of the second substrate and landing pad 251 isbonded to the contact pad on the underside of lip 250, the bottomsurface of the second substrate is substantially coplanar to bottomsurface 219 of interconnect structure 249.

In step 264, thermal interface material 220 is placed over the uppersurface of heat sink 221. The upper surface of heat sink 221 need not beplanar except under substrate 206 and the area directly around thesubstrate. For example, the upper surface of heat sink 221 can be themostly curved surface of a luminaire. Likewise, bottom surface 210 ofsubstrate 206 and bottom surface 219 of interconnect structure 249 neednot be coplanar except in the immediate vicinity of substrate 206.

In step 265, substrate 206 and interconnect structure 249 are placedover thermal interface material 220 such that thermal interface material220 contacts both bottom surface 210 of substrate 206 and bottom surface219 of interconnect structure 249. When the method of FIG. 32 is used tomake an array product, the second substrate of photon building block 248is also placed over thermal interface material 220 such that thermalinterface material 220 contacts the bottom surface of the secondsubstrate. The method of FIG. 32 can also be used to make an arrayproduct with more than two photon building blocks, such as the arrayproduct shown in FIG. 31.

FIGS. 33A-C are perspective views of embodiments of a photon buildingblock 269 similar to photon building block 204 of FIG. 20. FIGS. 33A-Bshow photon building block 269 without a lens in order better to showthe LED dies. FIG. 33C shows the photon building block 269 with asilicone lens structure molded over the LED dies.

Photon building block 269 contains nine LED dies as opposed to thesingle LED die of photon building block 204. The LED dies, includinglabeled LED die 207, are mounted on substrate 206 using silver epoxy.Landing pads 208 are disposed on the upper surface 209 of substrate 206.No electrical conductor passes from the upper surface 209 of substrate206 to the lower surface 210 of substrate 206. The LED dies areelectrically coupled to power solely through the landing pads 208. Inthe embodiment of FIG. 33A, the LED dies are electrically connectedthrough wire bonds 271 to the landing pads 208. The landing pads 208 aretraces made of a Cu—Ni—Au alloy or a Cu—Ni—Ag alloy. In anotherembodiment, the landing pads 208 are traces of silver-filled epoxy. Alayer 270 of a highly reflective (HR) material is disposed within a ring272 between and around the LED dies and the wire bonds 271 asillustrated in FIG. 33A. In the example of FIG. 33A, layer 270 of HRmaterial contacts the retaining ring 272 and also contacts the sides ofthe LED dies.

FIG. 33B shows another embodiment of photon building block 269 in whichthe LED dies are not connected through wire bonds 271 all the way to thelanding pads 208. Instead, short bonds wires from the LED dies connectto traces on near upper surface 209 that in turn are electricallyconnected to the landing pads 208. Groups of LED dies are also connectedin series to each other by bond wires 271.

FIG. 33C shows a lens structure 214 that has been molded over the nineLED dies. The lens structure 214 is molded over the LED dies before thephoton building blocks are segmented from the metal core printed circuitboard (MCPCB) that forms substrate 206. While the photon building blocksare still part of a single MCPCB as shown in FIG. 2, a thin conformallayer of a wavelength conversion material, such as a phosphor, isdeposited over the LED dies. For example, a conformal layer of siliconecontaining yellow phosphor 273 is formed over the LED dies. Thencompression molding is used to mold a clear resin encapsulant, such assilicone, over the LED dies and the wire bonds 271 such that a lens isformed over each LED die 207. In the embodiment of FIG. 33C, a separatemicro-lens is formed over the center of each of the nine LED dies. Mostof the upper surface 209 of substrate 206 can be occupied by the LEDdies and the associated lens structure because the mechanical andelectrical connections to a heat sink or luminaire have been removedfrom the photon building block and transferred to an interconnectstructure that supports the photon building block. In the embodiment ofFIG. 33C, there are less than three millimeters on the upper surface 209of substrate 206 between each edge of substrate 206 and a lens thatcovers one of the LED dies.

FIGS. 34A-B are cross-sectional views of photon building block 269 beingsupported by an interconnect structure 205 solely through the landingpads 208 on the upper surface 209 of substrate 206. The landing pads 208are both electrically and mechanically connected to contact pads 215disposed on the underside of a lip of the interconnect structure 205. Inone implementation, the landing pads 208 are attached to contact pads215 by a solder paste. An example of a solder paste is a SAC alloy, suchas SAC 305 (96.5% Sn, 3.0% Ag, 0.5% Cu). In a SAC reflow process thatoccurs in an upside down orientation to that shown in FIGS. 34A-B, thelanding pads 208 on substrate 206 self-align to the contact pads 215 oninterconnect structure 205. In a packaged LED array consisting ofinterconnect structure 205 and photon building block 269, substrate 206is electrically and mechanically connected to interconnect structure 205only through the landing pads 208 and the contact pads 215. Packaged LEDarrays in this condition are shipped from the LED manufacturer to theluminaire manufacturer. In another implementation, the landing pads 208are attached to contact pads 215 by an adhesive. An example of anadhesive is an anisotropic conductive adhesive associated withanisotropic conductive film (ACF) technology.

In the embodiment of FIG. 34A, the conductors over the top surface 217of interconnect structure 205 are metal traces 216. The contact pads 215that attach to the landing pads 208 are also metal traces. Metallizationbaths plate the traces 216 and contacts pad 215 over the interconnectstructure 205. A through-hole via 218 electrically couples metal trace216 to contact pad 215.

In the embodiment of FIG. 34B, the contact pads 215 that attach to thelanding pads 208 are written onto the surface of interconnect structure205 with a laser. In addition, the conductive paths on the surface ofthe interconnect structure 205 are formed using the same laser process.The molded interconnect structure 205 is formed from a thermoplasticthat contains a metal additive. A conductive path 226 is formed by themetal additive where the laser beam oblates the thermoplastic on thesurface of the interconnect structure 205. The metal particles in theconductive path also form nuclei for optional subsequent metallizationof the conductive path. In the embodiment of FIG. 34B, the laser hasoblated a continuous conductive path 226 across top surface 217, aroundthe lip 223 to the underside of the lip to form contact pad 215. Theconductive path is widened on top surface 217 to form contact pads towhich power and ground wires can be attached. In this manner, no vias orinternal metal layers are required in the molded interconnect structure205 of FIG. 34B.

FIG. 34B shows an implementation in which a conformal layer of siliconecontaining yellow phosphor 273 is formed over the LED dies. Greenphosphor 274 is dispersed in the silicone that forms lenses over the LEDdies. And a conformal layer of silicone containing red phosphor 275 isdeposited over the lenses.

FIGS. 35A-B are perspective views of the bottom and top sides,respectively, of an interconnect structure 276 that supports photonbuilding block 269 of FIG. 33C. Molded interconnect structure 276 has ahexagonal star shape and supports photon building block 269 by thetop-side landing pads 208. There is an opening 277 in the middle ofmolded interconnect 276 from which the lenses of photon building block269 protrude. FIG. 35A shows the bottom surface 219 of moldedinterconnect structure 276 into which an indentation 278 has beenformed. Indentation 278 has the shape of substrate 206 of photonbuilding block 269. In the orientation of molded interconnect 276 shownin FIG. 35A, photon building block 269 is flipped over and inserted intoindentation 278 such that the top-side landing pads 208 attach to thecontact pads 215 that protrude out from the inner surface 279 ofindentation 278. Each contact pad 215 is the bottom of a cylindricalmetal via that extends from the inner surface 279 of indentation 278 tothe top surface 217 of interconnect structure 276. The top of eachcylindrical metal via is coupled to a rectangular contact pad 280 towhich power and ground wires can be attached. Two of the six contactpads 280 on top surface 217 of interconnect structure 276 form redundantconnections to a contact pad 215.

FIG. 35B shows a packaged LED array 281 made up of photon building block269 being supported from its top side by hexagonal star-shaped moldedinterconnect structure 276. FIG. 35B shows the top surface 217 of moldedinterconnect structure 276 and the lens structure 214 of photon buildingblock 269 protruding through opening 277. In the orientation of moldedinterconnect 276 shown in FIG. 35B, photon building block 269 isinserted up and into indentation 278 such that top surface 209 ofsubstrate 206 is placed under inner surface 279 of indentation 278. Inso doing, a landing pad 208 is placed under and adjacent to a contactpad 215. The outer edges of flash layer 16 of silicone are sandwichedbetween top surface 209 and inner surface 279. The contact pads 215protrude out from the inner surface 279 of indentation 278 to bridge thewidth of the sandwiched flash layer 16 in order to make contact with thelanding pads 208. The landing pads 208 are then attached to the contactpads 215 using solder or a conductive adhesive. In an embodiment whereflash layer 16 is about fifty microns thick, the sum of the protrudingheight of contact pads 215 and the solder or adhesive that connectscontact pads 215 to landing pads 208 must also be fifty microns.Alternatively, the rim of inner surface 279 around opening 277 can berecessed to accommodate the thickness of flash layer 16. Photon buildingblock 269 is then aligned inside indentation 278 in a solder reflowstep. In the inverted orientation of FIG. 35A, molten solder on eachlanding pad 208 aligns over the contact pad 215 below.

FIG. 36A shows a packaged LED array 282 in which photon building block269 is supported by a hexagonal molded leadframe structure 283 that hasonly two of the six screw indentations 284 of the star-shapedinterconnect structure 276. Metal vias connect contact pads 285 on topsurface 217 of molded leadframe structure 283 to contact pads 215 in theindentation 278 on the back side of the structure. Molded leadframestructure 283 also includes side pads 286 that are disposed at a lowerlevel than top surface 217. The side pads 286 are disposed on a moldedshelf 287 that extends from a longer side of the hexagonal leadframestructure 283. Power and ground wires 288 may be soldered to the sidepads 286 such that the thickness of the insulated wires fits between theplanes of the upper surface 217 and bottom surface 219 of moldedleadframe structure 283. The side pads 286 are electrically coupled tothe contact pads 285 by conductive layers within the molded leadframestructure 283.

FIG. 36B shows the indentation 278 on the bottom side of moldedleadframe structure 283 into which photon building block 269 fits. Thecontact pads 215 are elevated somewhat from the inner surface 279 ofindentation 278 and are coupled to the contact pads 285 on top surface217 of molded leadframe structure 283.

FIG. 37A shows a packaged LED array 289 in which photon building block269 is supported by a hexagonal molded interconnect structure 290 thathas only two of the six screw indentations 284 of the star-shapedinterconnect structure 276. Interconnect structure 290 does not have thecylindrical metal vias of molded leadframe structure 283. Instead, thecontact pads 215 in the indentation 278 and the contact pads 285 on topsurface 217 are formed by writing conductive areas using a laser asillustrated in FIG. 34B. Each contact pad 285 on top surface 217 iselectrically coupled to a contact pad 215 on the bottom side of moldedinterconnect 290 by a conductive path 226 that extends across topsurface 217, around the rounded edge of opening 277 and then on innersurface 279 to a contact pad 215. Interconnect structure 290 alsoincludes the side pads 286 on molded shelf 287. The side pads 286 areelectrically coupled to the contact pads 285 by conductive paths 291that are written using a laser across upper surface 217 and a side ofthe interconnect structure 290. The laser is also used to write the sidepads 286 onto molded shelf 287. Interconnect structure 290 has no viasor internal metal layers.

FIGS. 37B-C are perspective views of the top and bottom sides,respectively, of an hexagonal molded interconnect structure 292 that hasbeen molded around lead frame conductors. FIG. 37B shows interconnectstructure 292 supporting a photon building block 293 with a single lensthat covers an array of LED dies. Together, molded interconnect 292 andphoton building block 293 comprise a packaged LED array 294. Unlikeinterconnect structure 290 of FIG. 37A, interconnect structure 292 hasinternal metal conductors formed from a metal lead frame around whichplastic has been molded. The side pads 295 on molded shelf 287 are partof the lead frame.

FIG. 37C shows the indentation 278 on the bottom side of interconnectstructure 292 into which photon building block 293 fits. The contactpads 215 are elevated somewhat from the inner surface 279 of indentation278 and are part of a lead frame layer of conductors. Two contact pads215 and one side pad 295 are part of the same lead frame conductor 296,as shown in FIG. 38. The lead frame is made of a thin sheet of metalfrom which the lead frame conductors are stamped. For example, a 0.1 mmsheet of a copper-nickel-palladium alloy can be used to make the leadframe. The lead frame is rolled onto a reel 297 and then unrolled asindividual interconnect structures are molded around each template 298of conductors. After individual interconnect structures are formed, theconnection from the lead frame reel to the side pads 295 is cut. Thephoton building blocks are then inserted into the indentations in areel-to-reel process before a solder reflow step aligns the landing padsof the photon building blocks to the contact pads of the interconnectstructures.

There are many different types of LED assemblies. FIG. 39 (prior art) isa top-down diagram of one such LED assembly 300. LED assembly 300includes four laterally-contacted LED dices 302-305 that are mounted ona metal core substrate 306. Substrate 306 in this case is a metal coreprinted circuit board (MCPCB). Areas 307-310 illustrated in dashed linesrepresent portions of a metal layer that is disposed underneath a soldermask layer 311 (see FIG. 40). Reference numeral 312 identifies a portionof metal portion 307 that is exposed through a first opening in thesolder mask layer 311. Similarly, reference numeral 313 identifies aportion of metal portion 308 that is exposed through a second opening insolder mask layer 311. These exposed portions 312 and 313 serve as bondpads. Ring structure 314 is a retaining ring of silicone. An amount of amaterial often referred to as phosphor 315 is disposed within the ringstructure 314 over the LED dice. This phosphor actually comprisessilicone and particles of phosphor that are embedded in the silicone.

FIG. 40 (prior art) is a simplified cross-sectional diagram of LEDassembly 300 of FIG. 39. MCPCB 306 includes an aluminum layer 316, aglobal dielectric layer 317, a layer 318 of metallization of which metalportions 307-310 are parts, and solder mask layer 311. Layer 318 ofmetal may involve multiple sublayers of metal including an upper layerof a very reflective metal such as silver. Metal portion 310 is a squarepad of metal upon which the LED dice 302-305 are mounted. The LED dice302-305 are fixed to pad 310 by associated amounts of silver epoxy.Amount 319 of silver epoxy is shown fixing LED die 304 to pad 310.Amount 320 of silver epoxy is shown fixing LED die 305 of pad 310.Reference numerals 321-323 identify wire bonds.

A layer 324 of a highly reflective (HR) material is disposed within ring314 between and around the dice 302-305 and wire bonds 321-323 asillustrated. The diagram is simplified in that the regions of the HRmaterial have smooth and rounded edges. Some of the light emitted by LEDdice 302-305 may be absorbed by phosphor particles in phosphor 315.These particles may then fluoresce and re-emit light such that thislight is directed downward, rather than upward as is desired. Referencenumeral 335 identifies one such particle of phosphor. A light ray 336 isemitted from the top of LED die 304 and travels up and is absorbed byparticle 335. A second light ray 337 is then emitted from particle 335and this second light ray travels back downward as shown. HR material324 is provided so that this light ray will be reflected so that it canpass upward and out of the assembly as light ray 338. Particle 335 isbut one such particle. There are numerous particles dispersed throughoutthe silicone material of phosphor 315. Light emitted from the LED dice302-305 can be emitted in various different directions including out ofthe sides of the LED dice. Similarly, a light ray emitted from aphosphor particle can travel away from the particle any direction. Theillustration of particle 335, of the direction of light emission fromparticle 335, and of the associated light rays 336, 337 and 338 in FIG.40 are only representative of one such particle and its associated lightrays. An example of an HR material is a silicone material that iscommercially available from ShinEtsu Chemical Co. Ltd. of Tokyo, Japan.

FIGS. 41-48 (prior art) illustrate a prior art method of manufacturingthe LED assembly 300 of FIG. 39. FIG. 41 (prior art) is a top-downdiagram of a panel 325 of MCPCBs. MCPCB 306 is one of the MCPCBs of thepanel. FIG. 42 (prior art) is a top-down diagram of the pad portion 310of the MCPCB portion 306 of panel 325. This pad portion 310 is exposedthrough an opening in the solder mask layer 311. FIG. 43 (prior art) isan illustration of a screen printing mask 326 used in the next step offorming the layer 324 of highly reflective (HR) material. FIG. 44 (priorart) is a diagram that shows the result of using the screen printingmask 326 of FIG. 43 to deposit the HR layer 324 onto panel 325. HRmaterial of layer 324 is deposited in the shaded circular region. Thiscircular region is in the center of MCPCB 306. As illustrated, there areeight windows 327-334 in the circular HR layer 324. FIG. 45 (prior art)is a diagram that shows the result of a next die attach step. Each ofthe four dice 302-305 is attached by an amount of silver epoxy in acorresponding one of the four center windows 327-330 in the HR layer 24.Each of the openings 327-330 in the HR layer is slightly larger than itsassociated die in order to accommodate variations in physical dimensionsand inaccuracies of the placement of the dice and wire bonds. FIG. 46(prior art) is a diagram that shows the result of a next step ofattaching wire bonds. Only three of the wire bonds 321-323 areidentified in the diagram with reference numerals. Some of the wirebonds extend between dice. Others of the wire bonds extend from a die toa conductive upper layer of the substrate. FIG. 47 (prior art) shows theresult of a next step of forming retaining ring 314. Retaining ring 314is formed so that it encircles the circular layer 324 of HR material asillustrated. FIG. 48 (prior art) shows the result of a next step ofplacing the phosphor 315 over the LED dice 302-305 in the area boundedby retaining ring 314. After the phosphor 315 has cured, the panel 325is singulated to form multiple LED assemblies of which LED assembly 300is one.

FIG. 49 is a simplified top-down diagram of a white LED assembly 340 inaccordance with one novel aspect. LED assembly 340 includes fourlaterally-contacted LED dice 341-344 that are mounted on a substrate345. In the present example, the substrate is a metal core printedcircuit board (MCPCB). Areas 346-349 illustrated in dashed linesrepresent portions of a metal layer 357 that is disposed underneath asolder mask layer 350 (see FIG. 50). Reference numeral 351 identifies aportion of metal portion 346 that is exposed through a first opening insolder mask layer 350. Reference numeral 352 identifies a portion ofmetal portion 347 that is exposed through a second opening in soldermask layer 350. These exposed portions 351 and 352 serve as bond pads.Ring structure 353 is a retaining ring of silicone. An amount ofphosphor 354 is disposed within the ring structure 353 over the LEDdice. This phosphor actually comprises silicone and particles ofphosphor that are embedded in the silicone.

FIG. 50 is a simplified cross-sectional side view of the LED assembly 50of FIG. 49. MCPCB 345 includes an aluminum layer 355, a globaldielectric layer 356, a layer 357 of metallization, and solder masklayer 350. Metal portions 346-349 are parts of layer 357. Layer 357 ofmetal involves multiple sublayers of metal including a lower layer ofcopper, a middle layer of nickel, and an upper layer of a veryreflective metal such as silver. Metal portion 349 is a square pad ofmetal upon which the LED dice 341-344 are mounted. The LED dice arelaterally-contacted blue LED devices whose epitaxial layers arefabricated on an insulative sapphire substrate. LED dice 341-344 arefixed to pad 349 by associated amounts of silver epoxy. Amount 358 ofsilver epoxy is shown fixing LED die 343 to pad 349. Amount 359 ofsilver epoxy is shown fixing LED die 344 of pad 349. Reference numerals360-362 identify three of the wire bonds seen in top-down perspective inFIG. 49.

A layer 363 of a highly reflective (HR) material is disposed within ring353 between and around the dice and the wire bonds as illustrated. Inthe example of FIG. 50, the layer 363 contacts the retaining ring 353and also contacts the side edges of the LED dice 341-344.

FIGS. 51-58 illustrate a method of manufacturing the LED assembly 340 ofFIG. 49.

FIG. 51 is a top-down diagram of a panel 364 of MCPCBs. MCPCB 345 is oneof the MCPCBs of the panel.

FIG. 52 is a top-down diagram of the pad portion 349 of the MCPCB 345 ofpanel 364. This pad portion 349 is exposed through an opening in thesolder mask layer 350. The metal surfaces of the panel are plasmacleaned. The corners 349A-349D serve as fiducial markers used in laterassembly steps.

FIG. 53 shows the result of the next step of the method. LED dice341-344 are placed and bonded to pad portion 349 as illustrated. Eachdie is bonded to pad portion 349 by an associated amount of silverepoxy. The bond line thickness (distance between the bottom of the dieand the top of the substrate surface) is less than 12 microns, and it istypically about 8 microns.

FIG. 54 shows the result of the next step of the method. Wire bonds areattached. Some of these wire bonds extend between dice. Others of thewire bonds extend from a die to a conductive upper layer of thesubstrate. Reference numerals 360-362 identify three of the wire bonds.The wire bonds may be sections of 1 mil diameter gold wire.

FIG. 55 shows the result of the next step of the method. Retaining ring353 is formed on the structure as shown.

FIG. 56 illustrates a next step in the method in which layer 363 of HRmaterial is deposited. In one example, layer 363 of HR material isdeposited using a jetting process. Microdots of HR material are jettedout of a jet head 365 so that the microdots travel toward the substrate345 (MCPCB) and impact the substrate, thereby effectively painting thesurface of the substrate with HR material. The liquid HR material doesnot flow under the LED dice due to the silver epoxy bonding materialoccupying this space. The jet head 365 is moved across the surface ofthe assembly of FIG. 55 as microdots of HR material are shot at thesubstrate so that areas of the surface of the substrate around the dice,and between the dice, and within the confines of circular retaining ring353 are painted with HR material, but such that the top surfaces of thedice and the top surfaces of the wire bonds are not painted. One ofthese microdots is identified with reference numeral 366 in FIG. 56.Arrow 367 indicates the path of its travel from jet head 365 toward thesurface of the substrate. In one example, each microdot has a diameterof less than 100 microns and is typically 50-80 microns in diameter. Thelayer 363 is deposited to be at least 10 microns thick. Arrows 371identify this thickness. In the illustrated example, layer 363 is fiftymicrons thick. The distance 369 between the bottom of the jet head 365and the upper extent of the wire bonds is approximately 500 microns. Inthis example, the distance 368 between the bottom of the jet head 365and the upper surface of metal layer 357 (including pad 349) isapproximately 1000 microns. In this example, the distance 370 betweenthe bottom of the jet head 365 and the upper surface of retaining ring353 is approximately 500 microns.

The HR material being jetted is made to have a predetermined andcontrolled viscosity such that the liquid HR material will flowlaterally somewhat across the surface being painted before the HRmaterial cures and solidifies. Due to this flowing action, microdots ofliquid HR material are fired onto the substrate surface near to a wirebond. The liquid HR material once on the substrate surface then flowslaterally underneath the wire bond so that after the step of depositingthe HR material is completed the HR layer 363 coats the surfaces ofsubstrate 345 (MCPCB) that are directly underneath wire bonds. At an endof a wire bond where the wire bond contacts the substrate, the entirecircular circumference of the wire is contacting HR material. Similarly,due to the predetermined viscosity of the liquid HR material, the HRmaterial flows laterally such that it reaches and wets the side edges ofthe LED dice 341-344 as illustrated. Reference numeral 372 identifies aside edge of LED die 343. In this example, only the bottom sapphireportion of the side edge 372 is wetted. The upper epitaxial portion ofthe side edge 372 is not wetted. Similarly, the HR material is made toflow laterally and to wet the inside side edge of the retaining ring 353as illustrated. Reference numeral 373 identifies the inside side edge ofretaining ring 353. The HR material is deposited with such a thicknessthat once it has cured and solidified it has a reflectivity of at leasteighty-five percent (for example, 94 percent).

In one example, the HR material is the material KER-2010-DAM or materialKER-2020 that is commercially available from ShinEtsu Chemical Co. Ltd.of Tokyo, Japan. The HR material may comprise silicone and a titaniumdioxide powder, where the titanium dioxide powder is suspended in thesilicone. The HR material is made jettable by cutting it with a solvent.In one example, the solvent is an oil-based solvent such asdimethylformamide (DMF) commercially available from ShinEtsu asDMF0.65CS. The HR material after being appropriately cut with thesolvent has a viscosity less than 1100 centipois (cP) at roomtemperature and in this example has a viscosity of 1000 cP at roomtemperature. In one example, the jetting equipment used to jet the HRmaterial is an Asymtek X1020 jetting machine available from HordsonAsmtek of 2747 Loker Avenue West, Carlsbad, Calif. 92010. The jettingmachine has two jet heads. The first jet head is used to apply HRmaterial with a first viscosity, whereas the second jet head is used toapply HR material with a second viscosity.

FIG. 57 shows the result of the step of depositing the HR material.Layer 363 of HR material covers substantially all the area within theconfines of the retaining ring 353 other than the top surfaces of LEDdice 341-344. Layer 363 coats the upper surface of the substrateunderneath the bridging bond wires. Whereas in the prior art example ofFIG. 47 there exists a peripheral strip of the substrate around each LEDdie that is not covered with HR material, in the structure illustratedin FIG. 57 there is no such uncovered peripheral strip. Whereas in theprior art example of FIG. 47 there are uncovered areas of the substratein the areas where wire bonds attach to the substrate, in the structureillustrated in FIG. 57 there are no such uncovered areas. The HRmaterial is made to coat the upper surface of the substrate right uplocation where the wire bond makes contact with the substrate. The HRmaterial is also made to coat the upper surface of the substrate rightup to the side edges of the LED dice. The HR material is made to coatthe upper surface of the substrate right up to the inside side edge ofthe retaining ring 353.

FIG. 58 shows the result of the next step in the method. Phosphor 354 isdeposited into the circular area bounded by the retaining ring 353 sothat the phosphor 354 covers the LED dice as illustrated in FIG. 50. Thephosphor is then allowed to cure and harden. Once the phosphor 354 hasbeen deposited, the panel of MCPCBs is singulated, thereby forming aplurality of LED assemblies. The LED assembly structure 340 illustratedin FIG. 49 is one of these LED assemblies.

The method set forth above in connection with FIGS. 49-58 has severaladvantageous aspects in comparison with the prior art method set forthabove in connection with FIGS. 39-48. First, the amount of the uppersurface of the substrate that is left uncovered by HR material isreduced in comparison with the prior art screen printing method. Partsof the substrate that are not covered by HR material may and typicallydo absorb light or otherwise do not reflect light well, thereby reducingthe light efficiency of the LED assembly. By covering more of thesurface of the substrate with HR material using the jetting process,more light is reflected from the LED assembly and the light efficiencyof the LED assembly is increased. In the prior art screen printingprocess used to deposit HR material, variations in physical sizes andimperfections in die attach and wire bonding processes required thewindows in the HR layer to be so large that after die attach and wirebonding substantial areas of exposed substrate remained uncovered by HRmaterial. In the jetting process, the HR material is applied after dieplacement and wire bonding, and machine vision and control techniquesare used to control the jetting process so that the substrate is coatedup to the edges of structures (the LED dice and the retaining ring) evenif the structures are in slightly different places, from one assembly tothe next. The use of laterally flowing HR material reduces the need toaccount for differences in die placement and wire bond locations fromassembly to assembly. The HR material naturally flows laterally up tothe proper structures even if the structures are not always disposed inthe same location from assembly to assembly.

Second, the HR layer is deposited after the sensitive die attach andwire bonding process steps. In the prior art screen printing method ofdepositing HR material, on the other hand, the HR material is screenprinted onto the substrate prior to die attach and wire bonding. The HRmaterial is an organic material. If die attach and wire bonding areperformed when organic residue is present on the substrate, then errorsin die attach and wire bonding can occur and such error reduce LEDassembly manufacturing yield. Accordingly, plasma cleaning is oftenconventionally done after the HR screen printing step in an attempt toremove all such organic residue prior to die attach and wire bonding.This plasma cleaning is, however, difficult to perform as compared toperforming die attach on a plasma cleaned surface that has never beenexposed to organics. Accordingly, defects due to performing die attachand wire bonding on surfaces having organic residues are reduced oreliminated using the jetting process.

Third, the jetted HR layer can be made to coat surfaces with relativelylarge steps and with different levels and sloped surfaces. In the priorart screen printing method, on the other hand, the surfaces to which theHR material is being applied must be more planar. In one example of thenovel jetting process, a first HR material with less viscosity isapplied to certain areas of the substrate that are relatively flat andplanar so that the HR material will flow under wire bonds and will flowup to the edges of dice, whereas a second HR material with moreviscosity is applied to other portions of the surface of the substratethat are more inclined or more stepped. The first HR material is appliedwith a first jet head of the jetting machine, whereas the second HRmaterial is applied with a second jet head of the jetting machine.

Fourth, the production rate of LED assemblies is increased by notcoating certain parts of the substrate with HR material in certainsituations. In some examples, the area of the substrate between LED diceis small. It has been found that the benefit of coating this smallinter-dice area is only slight. Accordingly, the HR material is notjetted into the inter-dice areas in order to save manufacturing time.

Fifth, it is generally desirable to be able to place fiducial markers onthe substrate surface and to have the imaging systems of the die attachand wire bonding equipment use these fiducial markers during die attachand wire bonding processing. In the prior art screen printing processwhere the HR layer has been deposited prior to die attach and wirebonding, there is limited exposed substrate area available for placementof appropriate fiducial markers. Most of the upper surface of thesubstrate has been covered by HR material. In the novel jetting methodof applying HR material, on the other hand, die attach and wire bondingoccur prior to the depositing of the HR layer. Accordingly, fiducialmarkers (for example, 349A-349D) that will later be covered over by HRmaterial are nevertheless usable at die attach and wire bonding time bydie attach and wire bonding imaging systems.

The deposition of an HR layer using jetting is not limited to theparticular LED assembly set forth FIG. 50. FIG. 59 is a diagram ofanother type of LED assembly 375. In the diagrams of FIG. 59 and FIG.50, the same reference numerals are used to denote the same or similarstructures. In the LED assembly of FIG. 59, the substrate 345 forms awell 376. The upper surface of the substrate has a nonplanar shape. Thefour LED dice 341-344 are mounted to metal pad 349 at the bottom of thewell 376 as illustrated. Jetting is used to coat the sidewalls of thiswell with HR material. In the specific example illustrated,substantially all of the upper surface of the substrate within thecircular confines of retaining ring 353 but for the LED dice 341-344 iscoated with HR material. The liquid HR material that is painted onto thesidewalls of the well can be a liquid HR material with a relativelyhigher viscosity as compared with the viscosity of the liquid HRmaterial that is painted onto the remainder of the surface of thesubstrate. The resulting HR layer is conformal to the nonplanar uppersurface of the substrate over the various edges and sloping surfaces ofthe substrate.

FIG. 60 is a diagram of another type of LED assembly 377. The substrate345 in this case includes a ceramic portion 378. A first electrode 379(P+ electrode), a second electrode 380 (N− electrode), and a thermal pad381 of metal are disposed on the bottom surface of the ceramic portion378. A conductive via 282 couples the P+ electrode 379 to metal portion348 on the upper surface of the ceramic portion 378. Similarly, aconductive via 383 couples the N− electrode 380 to metal portion 346 onthe upper surface of the ceramic portion 378. The thickness of the metallayers on the top and bottom of the substrate may be large, such aseighty microns, and this large thickness makes screen printing the HRmaterial difficult. The HR layer 363 contacts substantially all of atleast one side edge of each LED die as pictured. In the illustratedexample, the surface area of the substrate 345 between LED dice 341-344is not covered with HR material as described above in order to reduceproduction times. The inter-dice distance between the LED dice 341-344is less than 300 microns, and the inter-dice area is not jetted with HRmaterial. In other examples, this inter-dice area is coated with HRmaterial. In an example where a retaining ring is provided (not shown),the HR layer 363 may or may not extend outward all the way to theretaining ring. The HR layer 363 may contact the inside side edge ofsuch a retaining ring, or may stop short of the retaining ring such thatthe HR layer 363 does not touch the inside side edge of the retainingring.

FIG. 61 is a diagram of an LED assembly 384 where the substrate 345involves a ceramic portion 378 as in FIG. 60, but the HR layer 363 doesnot contact a side edge of any of the LED dice 341-344. The HR layer 363is deposited to stop short of the LED dice so that the HR layer 363 doesnot contact any side edge of any LED die. In the final assembly, the LEDdice appear disposed in a central window in the HR layer 363. Ascompared the screen printing conventional method of applying HRmaterial, however, the amount of exposed substrate (substrate under thephosphor 354 that is not covered by either an LED die or HR material) ismuch reduced in the structures of both FIG. 60 and FIG. 61.

FIG. 62 is a flowchart of a method 385. Initially, a substrate iscleaned (step 386) as necessary. In one example, the substrate 345 ispart of the panel 364 of FIG. 51. Panel 364 is plasma cleaned to removeany organic materials from its surface. Next (step 387), a plurality ofLED dice are attached to the substrate. In one example, the LED dice arethe dice 341-344 that are attached using silver epoxy to the substrate345. FIG. 53 shows the result of this die attach step. Next (step 388),wire bonding is performed as necessary. In some cases, wire bonding isnot used and the die is electrically connected to the substrate withoutwire bonding. In an example where wire bonding is performed, the resultof the wire bonding step is as shown in FIG. 54. Next (step 389), aretaining ring is formed around the LED dice as necessary. In oneexample where a retaining ring 353 is used, the result of the step offorming the retaining ring is as illustrated in FIG. 55. Next (step390), a layer of an HR material is deposited onto the substrate 345 suchthat the HR material does not cover the LED dice. FIG. 56 shows oneexample of how this HR material might be deposited in a jetting process.The HR material is jetted onto exposed portions of the upper surface ofthe substrate around the dice 341-344, and the liquid HR material isallowed to cure and harden. Next (step 391), an amount of liquidphosphor (actually silicone bearing phosphor particles) is placed overthe LED dice and allowed to cure. In one example, the result of thisstep is illustrated in FIG. 58. The resulting panel of LED assemblies isthen singulated (segmented) to form a plurality of separate LEDassemblies. In one example, FIG. 49 is a top-down diagram of one ofthese separate LED assemblies. In a first novel aspect, the HR layer ofthe LED assembly is deposited after the die attach step and after thewire bonding step in the LED assembly process. In a second novel aspect,the HR layer of an LED assembly is deposited by jetting microdots ofliquid HR material onto a substrate of the LED assembly.

Although certain specific embodiments are described above forinstructional purposes, the teachings of this patent document havegeneral applicability and are not limited to the specific embodimentsdescribed above. Accordingly, various modifications, adaptations, andcombinations of various features of the described embodiments can bepracticed without departing from the scope of the invention as set forthin the claims.

What is claimed is:
 1. A method comprising: mounting a first lightemitting diode (LED) die on a first substrate, wherein the firstsubstrate has a top surface, a bottom surface and a lateral boundary,wherein a plurality of landing pads are disposed on the top surface ofthe first substrate, and wherein no electrical conductor passes from thetop surface of the first substrate to the bottom surface of the firstsubstrate; placing a first lip of an interconnect structure over the topsurface of the first substrate and within the lateral boundary, whereina plurality of contact pads are disposed on an underside of the firstlip of the interconnect structure, wherein the interconnect structurehas a bottom surface, and wherein the bottom surface of the interconnectstructure and the bottom surface of the first substrate aresubstantially coplanar after the first lip is placed over the topsurface; and electrically and mechanically connecting the firstsubstrate to the interconnect structure only by connecting the landingpads to the contact pads.
 2. The method of claim 1, further comprising:placing a second lip of the interconnect structure over a top surface ofa second substrate, wherein the bottom surface of the interconnectstructure and a bottom surface of the second substrate are substantiallycoplanar after the second lip is placed over the top surface of thesecond substrate; and electrically connecting a conductor of theinterconnect structure to a second LED die disposed on the secondsubstrate, wherein the second substrate has dimensions that aresubstantially identical to those of the first substrate, and wherein thesecond LED die has dimensions that are substantially identical to thoseof the first LED die.
 3. The method of claim 1, wherein the interconnectstructure is taken from the group consisting of: a molded interconnectdevice (MID), an FR-4 epoxy circuit board, and a lead frame structure.4. The method of claim 1, further comprising: placing a thermalinterface material over an upper surface of a heat sink; and placing thefirst substrate and the interconnect structure over the thermalinterface material such that the thermal interface material contactsboth the bottom surface of the first substrate and the bottom surface ofthe interconnect structure.
 5. The method of claim 1, wherein the firstsubstrate is connected to the interconnect structure by heating thelanding pads such that each of the landing pads aligns with one of thecontact pads.
 6. The method of claim 1, wherein the interconnectstructure includes a conductor, and wherein after heating the landingpads the conductor of the interconnect structure is electrically coupledto the first LED die.
 7. The method of claim 1, wherein the interconnectstructure includes a conductor, wherein the landing pads are connectedto the contact pads using an anisotropic conductive adhesive, andwherein the conductor of the interconnect structure is electricallycoupled to the first LED die through the anisotropic conductiveadhesive.
 8. The method of claim 7, wherein the anisotropic conductiveadhesive mechanically connects the first substrate to the interconnectstructure.
 9. The method of claim 1, wherein the landing pads areconnected to the contact pads using solder.
 10. A method comprising:mounting a light emitting diode (LED) die on a substrate, wherein thesubstrate has a top surface, a bottom surface and a lateral boundary,wherein a plurality of landing pads are disposed on the top surface ofthe substrate, and wherein no electrical conductor passes from the topsurface of the substrate to the bottom surface of the substrate; placinga lip of an interconnect structure over the top surface of the substrateand within the lateral boundary, wherein a plurality of contact pads aredisposed on an underside of the lip of the interconnect structure, andwherein the interconnect structure has a bottom surface; andelectrically and mechanically connecting the substrate to theinterconnect structure solely by connecting the landing pads to thecontact pads, wherein the bottom surface of the interconnect structureand the bottom surface of the substrate are substantially coplanar afterthe substrate is connected to the interconnect structure.
 11. The methodof claim 10, wherein the landing pads are connected to the contact padsusing solder.
 12. The method of claim 11, further comprising: aligningthe substrate with the interconnect structure using a solder reflowprocess.
 13. The method of claim 10, wherein the interconnect structureis taken from the group consisting of: a molded interconnect device(MID), an FR-4 epoxy circuit board, and a lead frame structure.
 14. Themethod of claim 10, further comprising: placing a thermal interfacematerial over an upper surface of a heat sink; and placing the substrateand the interconnect structure over the thermal interface material suchthat the thermal interface material contacts both the bottom surface ofthe substrate and the bottom surface of the interconnect structure. 15.The method of claim 10, wherein the substrate is connected to theinterconnect structure by heating the landing pads such that each of thelanding pads aligns with one of the contact pads.
 16. The method ofclaim 15, wherein the interconnect structure includes a conductor, andwherein after heating the landing pads the conductor of the interconnectstructure is electrically coupled to the LED die.
 17. The method ofclaim 10, wherein the interconnect structure includes a conductor,wherein the landing pads are connected to the contact pads using ananisotropic conductive adhesive, and wherein the conductor of theinterconnect structure is electrically coupled to the LED die throughthe anisotropic conductive adhesive.
 18. The method of claim 10, whereinthe anisotropic conductive adhesive mechanically connects the substrateto the interconnect structure.
 19. The method of claim 10, wherein thelip of the interconnect structure surrounds an opening in theinterconnect structure.